Every modern presidential runner-up has conceded defeat to the winner. One election winner, Al Gore, even famously conceded defeat to the runner-up. The concession speech isn’t just a custom or ritual of civility, but a critical signal to millions of voters that, though their candidate lost, the winner is the legitimate incoming leader of the country.

As a failsafe, it isn’t perfect. After every legitimate election in America, you can find a small bloc of voters from the losing party that refuses to accept the results. And every president must contend with a similarly small subset of the population that views the presidency as illegitimate—or even a terminal threat to the republic.

This is probably inevitable, even if losing parties typically do their best to tamp down their supporters’ conspiracy theories and bad feelings. But nearly 100 days before this election, Donald Trump is already doing the opposite.

Unlike every candidate who came before him, Trump is actively trying to maximize the number of voters who will reject the results of the election. As in so many of the controversies he’s stirred (his call for a ban on Muslim travel into the U.S., his repeated insistence that illegal immigrants are driving a spike in violent crime), he has taken the subtext of Republican rhetoric and made it explicit. But in this case, perhaps more than in others, what he’s doing threatens to undermine public faith in democratic processes on a mass scale, with unpredictable and potentially destabilizing consequences.

At a rally on Monday in Columbus, Ohio, he told the faithful, “I’m afraid the election’s gonna be rigged, I have to be honest,” before going on Fox News to tell Sean Hannity, “I’m telling you, November 8, we’d better be careful because that election is going to be rigged.”

This is likely just the start.

There is no telling what Trump will do or say on election night if, as expected, Hillary Clinton defeats him. But all along we’ve known two things: Trump can’t stand losing, and he steeps himself in right-wing grievance politics. Combined, they provide him the motive and the means—the vocabulary—to violate the fragile norms governing our elections. He’s stipulating in advance that Hillary Clinton is a crook—that if she wins, it means the election was stolen. And in so doing, he’s co-opting the language and tactics influential conservatives have been using, less overtly, to undermine President Obama and liberal governance for years.

Obviously, opposition parties can profit indirectly from the kind of mass denial, and thus the intense opposition, that Trump is trying to sow. During the Obama years, Republicans have done just that, in their own norm-violating way. They’ve vouchsafed conspiracy theories about the president’s birthplace, and insinuations that groups like the New Black Panthers (which barely exists) and ACORN (which no longer does) are intimidating Republicans out of voting or stuffing ballot boxes for Democrats.

For years now, too, Republicans have comically exaggerated the extent of election fraud, and voter-impersonation fraud in particular, to advance Voter ID and other state laws aimed at suppressing turnout. Lower turnout helps Republicans win elections, and the central criticism of these laws is that they systemically disenfranchise minority voters. But the strategy has another malign effect, which Trump is now amplifying: By lying about the scope of election fraud, Republicans have eroded their supporters’ faith in the integrity of the vote. They’ve laid a seedbed for sprouting doubts about the legitimacy of our elections, and Trump is now covering it with his own distinctive fertilizer.

The right has long attacked the legitimacy of liberal rule in other, subtler ways, too. It’s an article of faith among influential members of the conservative legal establishment that the liberal vision of a strong federal government—one that regulates industry and redistributes income—is fundamentally at odds with the Constitution. In the face of Trump’s utter indifference to constitutional limits on state power, many of these conservatives have nonetheless coopted the mantles of “rule of law” and “law and order,” the latter of which was an official theme of the Republican convention two weeks ago. The purpose here is to equate Republican rule with legitimacy, and Democratic rule with lawlessness and plunder.

For all his supposed deviations from GOP orthodoxy, Trump has unquestionably absorbed the language and conceits underpinning conservative opposition strategy—if not the finer points of it. Trump quite naturally feels entitled to appropriate that strategy in service of making excuses for his own likely defeat.

“The whole thing with voter identification I think is really—I mean people are going to walk in, they are going to vote 10 times maybe,” he told Bill O’Reilly on Tuesday.

If you want a demonstration of Trump’s Republican provenance, look no further than this statement, which uses GOP pro-voter ID language in service of protecting his own ego. It mimics the Republican Party platform, which falsely bemoans “a significant and growing form of voter fraud.”

But when this comes out of the mouth of a presidential nominee, it imperils one of our most vital traditions, the peaceful transition of power. And it’s put mainstream Republicans in a quandary of their own making: While Trump has taken their arguments a step too far, from delegitimizing liberal rule to delegitimizing democracy in a far more basic way, Republicans like House Speaker Paul Ryan have a stake in allowing Trump to undermine Clinton’s legitimacy in advance of her inauguration. They understand that Clinton will meet deeper-than-usual resistance to her agenda in the first months of her presidency if she enters office under a pall rather than with a mandate.

That may explain why, on top of refusing to repudiate an increasingly offensive and erratic Trump, Ryan has so far declined to stand up for the integrity of our elections. He may figure that at this early date he doesn’t have to. As the political scientist Brendan Nyhan has pointed out, “bipartisan consensus is the most powerful force in public opinion.” If Ryan and other Republican leaders validate the election results as soon as they’re clear, it will go a long way toward discrediting Trump’s efforts to undermine them. But by then, who knows how many millions of people will have been convinced that the process was perverted?

GOP leaders, heavily invested in avoiding a complete breakdown of party cohesion, are unlikely to disavow Trump before the election. But it will be a capstone to their disgrace if they allow this particular Trumpian affront to stand after all the votes are counted.