I mean, we've had exclusively Democrat or Republican governments for well over 150 years, I'm not sure how else you'd measure "total and perpetual dominance".

Let's imagine that this were to actually happen. Major members of the two parties realized that what you said was true, and that if they could cooperate then they would totally and completely dominate the political system, and could do whatever they wanted, no matter what the electorate said, and no matter how bad it was for those governed.

They would soon realize that there was a problem, in that the electorate like to have a choice, and would unquestionably form some sort of opposition to any government that tried to rule without offering a choice.

The solution they would come up with, in order to make this dominance happen, would be to offer the illusion of choice. So they would agree to offer the electorate two alternatives, ensuring their continued dominance in two ways:

1. Making the two 'alternatives' actually very similar. So rather than offering options that might be popular in other countries, such as increased healthcare or higher wages, offer two choices that differ only very slightly from each other.


2. Keep up the appearance of strong enmity between the parties, and couple it with a very complex and oppositional legislative system, with no way of resolving disputes if two parts of the legislature disagree. This ensures that there is always a good reason not to pass laws or make changes, no matter how popular. It's always the fault of that pesky other party that nothing can be done.

So that's what would probably happen if this was tried. I leave any conclusions to the reader.

In the US, the two parties comparative to most of Europe are not ideologically far apart. First-past-the-post elections tend to concentrate on winning the "independent" voter which has a tempering impact on ideological shift. What you are referring to has a name; it's called the uniparty that is generally benefits from Pax Americana and is globalist, free-trade, open-borders, and definitely pro-spending. Here's a snippet on the uniparty.

The Republican Party’s leaders have functioned as junior members of America’s single ruling party, the UniParty. Acting as the proverbial cockboat in the wake of the Democrats’ man-of-war, they have made Democratic priorities their own when the White House and the Congress were in the hands of Republicans as well as in those of Democrats, and when control has been mixed. The UniParty, the party of government, the party of Ins, continues to consist of the same people. The Outs are always the same people too: American conservatives. They don’t have a party.

Whatever differences exist within the Uniparty, between Republican John Boehner and Democrat Nancy Pelosi, between Republican Mitch McConnell and Democrat Harry Reid, get worked out behind closed doors. Those differences are narrow. The latest negotiations were over some $80 billion out of three trillion dollars in spending. The bipartisan negotiators did not let into the room any of the major issues that concern Americans. Not Obamacare, not racial preferences, not religious liberty, not endless no-win wars. The UniParty is unanimous: more of the same!

Here's some more from Politico

“The Uniparty” is the latest populist buzzword to seize the imagination of the drain-the-swamp crowd, those who see grand conspiracies in the machinations of the “deep state” and globalist-corporate forces. It has a crisp clarity, instantly conveying the idea of an establishment cabal, Democrat and Republican alike, arrayed against their outsider hero, Donald Trump.

But while “the Uniparty” may be trendy among the Breitbart set, it wasn’t born there. In fact, if you go back to the contentious presidential race of 2000, you’ll find it arose as a political barb among supporters of Ralph Nader, running as the nominee of the Green Party.

Numerous posts on the Usenet newsgroup alt.politics.green from that year railed against “the two-headed UniParty,” “the money-driven media/political uniparty environment,” “the corporate Uniparty grip on the civic polity,” and so forth.

This article also is really good

I actually upvoted K Dog's answer because "uniparty" is probably the hypothesis being advanced by the question (which itself is rather vague). But it's also easy to see why doesn't really work that way: primaries. It's easy for a party to change is position over time when its candidates are elected too, and that happens in the primaries. Just look how the Republican part of the "uniparty" got turned toward a new discourse by the Trump takeover. Not long before that was the Tea Party etc.

The "uniparty" only lasts as long as there's not a strong enough grassroots base for some divergent idea to be embraced by candidates in the primaries of one of the parties (but not the other). And there can be many such issues causing a divergence. And empirical data nicely shown in another question here actually points to a divergence rather than converges of the two main parties on ideology. The graph in the question linked is only about Congress, but there's separate data that that divergence really comes from the public divergence (i.e. it's not just some fight between two small cliques of politicians):

So you can't get a "uniparty" from that trend... unless the elections get subverted somehow.

The importance of the primaries in the US for the good functioning of the democracy as really representative is emphasized by the laws that provide public funding for primaries, etc., in order to prevent them from being a closed club.

let's turn the question around and assume that we already have such a situation where both parties have (at least de-facto) merged into a single Party. Then because the public opinion on many issues tends to have a 50-50 split due to social dynamics, this will cause tensions within the Party. Many issues will have a typical conservative or liberal points of view, so there will be strong correlations between Party members and their views; typically two party members will agree with each other on most issues or they will disagree with each other on most issues. This will then ultimately cause the Party to break-up into a liberal faction and a conservative faction.

This instability of a single Party state will then prevent two dominant parties from merging into a single Party.

This is so-called two steps forward, one step back approach in controlling population

You create two at first glance bitterly opposed parties that seemingly oppose each other on number of important issues. One party comes to power and impose some unpopular law or issue. Other party rides on wave of popular indignation with the measure, but when finally after elections comes to power does little or nothing to change situation. Instead, it repeats the cycle with some other unpopular act, and cycle repeats itself.

Other parties and other issues (which could be very important, but two major parties agree on them) are ignored by mass media, so voters do not know about them .

Examples from real life :
Most Americans started opposing Iraq war in 2005. War was Republican endeavor, and led to rise of Democrats and Obama who portrayed themselves as doves. But when Democrats took power, they actually increased US military involment around the world, especially in Middle East (Libya, Syria etc ...)

Most Americans opposed homosexual marriage in 2009. It was Democrats measure to push it on whole country, with lot of Republicans bitterly opposing it. But when Republicans finally took power in 2017 they declared that "homosexual marriage is law of the land" and did nothing to overturn this decision.

Large number of Americans oppose abortion, especially late-term abortion . In fact anti-abortionist are becoming majority lately. Republicans often campaign on this issue, and often enact some minor laws on state level that more usually then not get overturned by Federal judges. Yet, despite obvious problem (Roe v. Wade) , Republicans never muster an effort to define unborn children as humans (let's say from seventh week of pregnancy) , therefore giving them legal protection from killing.

As we could see from this example, both Republicans and Democrats act like different cycles of same engine that pushes US in direction not necessarily in interest of its population, and their largely ceremonial confrontation sucks the oxygen from other political movements.

Walter Karp argued that US political parties form a virtual bipartisan oligarchy which colludes together for the primary purposes of mutual self-preservation and maintaining organizational power in his 1973 Indispensable Enemies: The Politics of Misrule in America.

They did when they had a common external enemy, and the world was better for it.

The United States fought the fascists during World War II (1941-1945), and the Soviet Union during the Cold War (1945-1991). During this period, the country faced a common external enemy, and Democrats and Republicans cooperated to unprecedented levels. Among the accomplishments:

• Willingness from both political parties to engage in foreign affairs, form alliances, and negotiate treaties and trade pacts.


• Serving as a political and economic superpower.


• Actively participate in the United Nations and NATO.


• Aiding other countries through the International Monetary Fund and World Bank, which helped the reconstruction of much of Europe and Japan after WWII.


• Development of the Interstate Highway system.


• Funding (or in some cases, directly pursuing) scientific research through the National Science Foundation, National Institutes of Health, Department of Energy, and DARPA.


• Through DARPA, funding the initial development of the Internet that you are now using.


• Providing funding for public elementary, secondary, and higher education.


• Providing stable government institutions. As much as Reagan talked about cutting government, in practice most agencies grew during his tenure.


• Enthusiastically operating a space program -- and most notably -- putting men on the moon.

After the fall of the Soviet Union, the enemy became each other. Democrats and Republicans turned on each other, in increasing rounds of tit-for-tat. Indeed, during the last 25 years we have seen the following:

• Paranoia that the United Nations is a world government which is controlling American politics.


• Using foreign countries as a scapegoat for job losses.


• Isolationism.


• Withdrawal from NATO, NAFTA, TPP, and other alliances and trade pacts.


• The loss of international respect and influence of the United States.


• Cutting foreign aid (particularly for "s---hole countries").


• Deteriorating infrastructure (e.g. collapsed roads and bridges, contaminated public water supplies). Refusing to repair or replace it because of a fear of taxes and government spending.


• Cutting scientific funding (e.g. Superconducting Supercollider).


• Mocking science as an "opinion" (e.g. evolution, climate change, endangered species).


• Refusing to regulate the monopolies that control much of the Internet.


• Cutting funding for public elementary, secondary, and higher education (mostly by state governments).


• Turning education over to for-profit corporations.


• Mocking (e.g. "Deep State"), defunding, and harassing government institutions.


• Allowing the space program to wither to the point where we use Russian rockets to send astronauts into space.