James Downie is The Post’s digital opinions editor.

For months, political observers said over and over that the GOP front-runner wouldn’t win the nomination. But after accumulating seven more victories on Super Tuesday, bringing his total to 11 of the first 15 states, Donald Trump has destroyed that conventional wisdom and looks likely to be Hillary Clinton’s opponent in the fall.

And after getting it so wrong once, many prognosticators now seem worried about underestimating Trump’s chances in the general election. “Democrats to Clinton: Don’t laugh off Trump threat,” blared a Politico headline. “I’ve gone from denial,” Connecticut Gov. Dannel Malloy told the New York Times, “to admiration . . . to real worry.” Even Democrats projecting confidence about a Trump-Clinton matchup typically scramble to add an “on the other hand” disclaimer.

To borrow a phrase from one of the men trailing Trump: Let’s dispense with the notion that Trump has a real shot at winning in November.

Start with the basic electoral math. At the national level, Trump trails Clinton by more than three percentage points in the RealClearPolitics polling average, and she has led him in 15 of 17 national polls since December. Trump clearly does the worst against her of the possible Republican nominees. His unfavorables are historically high for a general election nominee. And if “more than three points” doesn’t sound impressive, note that Barack Obama rarely led Mitt Romney by more than three points in the polling averages — and he won easily. What state polling we have suggests that Clinton, like Obama, will start with 220 or 230 electoral votes safe or close to that amount, leaving Trump little room for error.

Insult after insult flew during the Fox News GOP debate on March 3. Here's a look at some of the choice words rivals Marco Rubio, Ted Cruz and Donald Trump had for each other, while John Kasich stayed out of the fray. (Jenny Starrs/The Washington Post)

Breaking the numbers down demographically makes Trump’s path look even steeper. In 2012, Romney easily won the non-Hispanic white vote, but it wasn’t nearly enough to overcome his poor showing among Hispanics, who broke 71 to 27 percent for Obama. A recent Post-Univision News poll found that 80 percent of Hispanics have an unfavorable view of Trump. Given that the electorate is expected to be less white than it was in 2012, Trump would have to win an unprecedented share of the white vote to stand a chance. Furthermore, Trump’s campaign has a poor record of setting up the competent field operations needed to boost turnout among his base of support.

Nor will the media advantage that has helped Trump in the Republican primaries carry over to the general election. As the rival party’s front-runner — and someone willing to take Trump on from the start — Clinton will have a much easier time getting her fair share of free media. In addition, barring a dramatic turn in the controversy over her State Department email, there isn’t much reason to think Clinton will struggle in the fall. Some have suggested that record turnout in the Republican primaries bodes ill for the Democrats come November. But there’s no historical evidence of such a connection. In 1980 and 1988, millions more people voted in the Democratic primaries than in the Republican contests — and Democrats lost in the fall. In 2000, Republicans had the edge, and the GOP lost the popular vote. And there’s no consistent relationship between increases or decreases in a party’s primary turnout from four years earlier and victory in November.

Some, on the other hand, worry that attacks on Trump for his long track record of lies and failures seem never to stick, or that he will be able to magically cast off the burden of his extremist stances by moving to the middle. But that’s what Democrats feared about Mitt Romney this time four years ago. Yet Latino voters did not forget about Romney’s call for self-deportation, and attacks on Romney as a corporate raider proved much more effective for Obama than they were for Romney’s foes in the GOP primary. Nor was Romney able to make voters forget the big gaps in his implausible budget and tax plan.

The strongest case for a November Trump surprise is that he has a unique appeal to working-class voters who feel left behind by both parties. Here, Clinton has Bernie Sanders to thank for preemptively pushing her in a more populist direction; if she maintains the populist rhetoric (and proposes more policies to match), she will blunt Trump’s advantage with fed-up voters.

It’s also worth noting that Clinton is most popular when the public thinks she is being unfairly attacked, as Rick Lazio, her hapless opponent in the 2000 New York Senate race, can attest. Who thinks Trump will go eight months without wildly crossing the line?

Democratic politicians and operatives have every reason to hype the Trump threat; fear of a Trump presidency would surely boost Democratic turnout in November, helping candidates up and down the ballot. But the rest of us don’t have to agree. Trump may have defied the conventional wisdom once. That doesn’t mean he’s likely to do it a second time.

Read more on this issue:

Ruth Marcus: I was wrong: President Trump would be way scarier than President Cruz

The Post’s View: Now is the time for Mr. Ryan and others to disavow Mr. Trump

Danielle Allen: Dear Jeb Bush: Help America stop Trump

Charles Lane: Trump wants to make America more like Denmark

E.J. Dionne Jr.: Trump traps the GOP