Many Americans are justifiably nervous that the know-nothing pathological narcissist at the top of the Republican ticket might actually win the presidency. Still, while this could indeed happen, it remains unlikely.

Perhaps the bigger fear, for both Democrats and plenty of Republicans, ought to be that the Republican Party will continue its long-durée drift off the ideological map and into uncharted territory long after Donald Trump goes down to defeat in November. Because in a two-party system, there is no question that at some point power will be returned to the GOP, even if the party can no longer be trusted to wield it responsibly in the public interest.

It wasn't always this way. Even while seeing their party captured by obstructionist ideologues, Republican voters continued to forward reasonable-seeming candidates as their presidential nominees. John McCain and Mitt Romney, despite being force-marched rightward by their own voters, were longstanding public servants, and even the manifestly incapable George W. Bush was a two-term governor with a narrow streak of tolerance that he maintained while his party went nativist. The willingness to place enormous power in the hands of Donald Trump, a hateful political neophyte with no grasp of policy and an unprecedented disregard for the norms of democracy, signals a new phase in the Republican Party's descent into madness.

Political scientists actually have a name for what the GOP has become: an anti-system party. The term was coined to describe parties — largely fascists on the right and communists on the left — that participated in European parliamentary democracies in order to annihilate them after attaining power.

Little known in America, the Italian political scientist Giovanni Sartori's seminal 1976 book, Parties and Party Systems, is still considered the best guide to understanding the dynamics of multiparty politics. In it he defined an anti-system party as one that seeks "not just to change the government, but the very system of government itself." The term has largely been used to describe explicitly anti-democratic parties that participate in politics, such as the Salafist Nour Party in post-uprising Egypt or the National Socialists in the Weimar Republic. The danger of such parties attaining power should be obvious.

Sartori's theory has two dimensions. The first is ideological — the party's stance vis-à-vis democracy. But we must also consider a party in terms of "relational anti-systemness" — the ideological distance between the party and other political actors in the system. As Sartori argued, "An anti-system opposition abides by a belief system that does not share the values of the political order within which it operates." A party, therefore, could still support democracy but careen so far ideologically from the other parties that it could be considered anti-system. Such anti-system parties are dangerous because of what Sartori called their "delegitimizing" impact on the system as a whole, which can be seen very clearly in the American public's sharp decline in trust and approval of our political institutions during the Obama presidency.

If one acknowledges that consensus and compromise ought to be baked into American democracy, then the contemporary GOP — or at least a large contingent of it — is an anti-system party. So many members of the GOP do not believe in the consensus norms and patterns of cooperative behavior that structure the system that they have brought national governance itself to a calamitous halt. Even Republican voters increasingly prefer to elect politicians who refuse to entertain accommodation.

Unlike in many parliamentary democracies, in which the majority party or coalition has carte blanche to enact legislation, American institutions almost always require cooperation between parties and branches to achieve legislative and policy goals. Some of these roadblocks — political scientists call them "veto points" — are part of the constitutional design, such as non-concurrent elections for Congress and the presidency and the "separation of powers" that appears to be the only governance concept taught to high school students in this country.

Other veto points were just made up, like the filibuster or the Hastert Rule, and treated like constitutional features of American democracy by people who seem not to know any better. Taken as a whole, they create a system that requires near-constant collaboration between the parties even for routine governance, except in the relatively rare circumstances where one party controls the presidency and both houses of Congress, including a 60-seat supermajority in the U.S. Senate.

The degree to which the contemporary GOP has moved away from the ideological center of American politics and the Democrats is worrisome. The average House Republican is so distant from the center as to make compromise even with center-right Democrats nearly impossible. Data on ideology and polarization have been maintained monkishly by political scientists Howard Rosenthal and Keith Poole since the 1980s. It shows, for instance, that the percentage of non-centrists in the House Republican caucus has gone from about 44 percent in 1999 to nearly 90 percent today, while the number of non-centrist Democrats has stayed almost exactly the same at about 10 percent. Since Ronald Reagan took office, the ideological distance between the parties has more than doubled.

The problem is not just the GOP's rightward voyage in policy preferences. One can be vehemently anti-tax and still vote for modest tax increases. But the GOP does not appear to believe in compromise with the Democrats even to achieve long-sought goals like raising the eligibility age for Medicare or slashing spending on social welfare. Increasingly, Republicans do not pursue compromise even with the few remaining so-called 'moderates' in their own party. They have zero interest in passing legislation that has any chance of getting signed by a Democratic president. This is a problem not just because it disgusts everyone who isn't a nihilist or a gun lobbyist, but also because American democracy is hurtling toward an apocalyptic showdown about legitimacy.

Most anti-system parties throughout history have been small, minority movements that have rarely captured power, such as European communists after World War II. The question facing most democracies of this period was whether such parties could be peacefully integrated into an existing system they wished to overthrow. Americans now face the troubling reality that an integral feature of our electoral order — one of two enormous, catch-all parties with tens of millions of committed supporters — is in the process of rejecting American democracy.

Trump is therefore not just the product of the conservative echo chamber, or the Tea Party aversion to pragmatic compromise. His rise is evidence that the party and its voters may soon fuse their increasingly anti-system behavior and preferences with a political figure who shares Trump's contempt for democracy but who also possesses the skills and temperament to make his dark vision a reality.

Sartori, whose country had been destroyed by such demagogues in the recent past, warned that while such parties are unlikely to thrive in the long run, "the political scientist may well have to discover that the 'long run' was too long for the living actors — and for the political system."

How long will America's long run be?