The conventional wisdom has calcified: Donald Trump is going to lose to Hillary Clinton.

Sure, there have been brief moments when the outcome seemed in doubt — when the FBI director called Clinton's handling of her emails while secretary of state "extremely careless"; when it looked for about a half-hour that Trump received a significant bump from the GOP convention. But for the most part, and especially in the month since the conclusion of the Democratic convention, the race has settled into a stable pattern, with Clinton running between 4 and 8 points ahead of Trump nationally and beating him in most, if not all, of the so-called swing states. Hence the conventional wisdom: Trump will lose.

But the conventional wisdom is wrong. Trump isn't merely going to lose. He's going to lose in the biggest popular vote landslide in modern presidential history.

Democrat George McGovern finished with 37.5 percent in his 1972 race against Richard Nixon, the lowest tally for a major party nominee in a two-person race since Republican Alf Landon pulled in 36.5 percent against FDR in 1936. (George H.W. Bush managed to win 37.4 percent in his 1992 contest against Bill Clinton and Ross Perot, with the latter coming in at 18.9 percent of the vote.) Trump is now on track to challenge all of these results. It's not crazy to think he'll finish with less than 35 percent of the popular vote.

The electoral map will be different. Trump will lose there, too — though unlike McGovern, who pulled in only 17 electoral votes, Trump is pretty much guaranteed a triple-digit tally of electoral votes thanks to overwhelming Republican dominance of states in the South, Midwest, and Intermountain West. The GOP could nominate a turnip and still win the South.

But the popular vote will tell the democratic truth: Trump may well end up being the most unpopular candidate from a major party since before the New Deal.

In the national popular vote, the RealClearPolitics average has Trump at 41.4 percent, while FiveThirtyEight estimates 42.5 percent. That's low, but not at all unprecedented, especially in a race with three or more serious competitors. Compared to Republican Barry Goldwater's 38.5 percent in 1964 and Democrat Walter Mondale's 40.6 percent in 1984, a Trump outcome of 42 percent would be far from humiliating.

But he isn't going to finish at 42 percent.

It's not because of Hillary Clinton's appeal as a candidate. Far from it. She's only polling in the mid-to-high 40s now. (RCP has her at 46.7 percent; FiveThirtyEight at 48 percent). That's about where she'll end up.

Trump, by contrast, is going to sink. Voters are just beginning to understand a lesson that will be driven home by the debates and the merciless barrage of ads that the Clinton campaign will unleash against the GOP nominee in the final month of the campaign: that the only consistency about Trump is that he will disappoint and humiliate anyone who comes to believe in him.

Trump invariably transforms supporters into suckers. And that is a recipe for a landslide loss.

The list of prominent Republicans humiliated by Trump is very, very long: from Jeb Bush and Marco Rubio on down to Paul Ryan and John McCain. That has left Trump with a smaller base of supporters than one would expect from a major party nominee in 2016. (Mitt Romney was averaging 2-3 percentage points higher than Trump at this point in the race.)

Now, many of those favoring Trump have been passionately devoted to the candidate. That is unlikely to persist through the trials that began roughly 10 days ago and are bound to continue over the coming weeks.

Trump has reversed himself on a long list of policies over the years. But the one constant since he announced his candidacy for president in June 2015 has been his anti-immigrant stance. He would build a wall along the southern border of the United States and forcibly deport as many as 11 million undocumented immigrants. He's made the point over and over again at countless campaign rallies and events and in dozens of interviews and debates over the past 14 months. He alone will fix the problem of illegal immigration, unlike the losers who support various forms of amnesty, including the path to citizenship contained in the Gang of 8's immigration bill, which Rubio co-wrote.

But now? As Ann Coulter learned on the eve of a book tour to promote her love letter to Trump for his all-around trustworthiness, especially on immigration, the GOP nominee is the most singularly unreliable figure in American politics, even on his signature issue. First Trump indicated that he doesn't think amnesty (in all but name) is really so bad after all. Then his surrogates made clear that his promised border wall and mass deportations might end up being more "virtual" than real. On Wednesday, Trump traveled to Mexico City, met with Mexico's president, apparently chickened out of backing up his long-held and loudly declared boasts of making Mexico pay for the border wall, and pronounced the country full of "great people." Just a few hours later, Trump delivered a furious tirade of a speech in Phoenix about the horrors of illegal immigration and assured the rowdy audience that Mexico would pay for "100 percent" of the border wall.

Who knows what to believe?

Between now and Election Day, Trump will surely offer up even more of a mish-mash of positions on immigration (along with every other issue), with some of them sounding like pivots to less extreme views and others reinforcing harsher stances. But it's already too late. There are now squishy sound bites to quote in debates and replay endlessly in campaign ads. Which is exactly what the Clinton camp will do over and over again. As the weeks go by, the hits are going to take a toll. They won't necessarily drive Trump's supporters into the hands of Gary Johnson or Evan McMullin, and they certainly won't inspire them to consider voting for Clinton. But Clinton doesn't need them to do that. She just needs them to stay home on Nov. 8. That's when Trump's failure to open field offices across the country is going to prove decisive — and fatal.

The most credulous members of the Trump fan club will show up to cast ballots for him no matter what he says and does. But the rest? An awful lot of them are likely to stay home out of simple self-respect. Precisely how many do so is what will make the difference between a loss and a historic wipeout.