Donald Trump becoming the presumptive Republican nominee is such a sui generis event that it’s hard to know what to make of it. He seems to be a weak general election candidate, but liberals conditioned to expect the worst may start to look for reasons why he’s stronger than he appears. Certainly, Trump’s victory over a deep slate of Republican rivals is evidence that we would be foolish to write him off too quickly. But when all is said and done, the impulse reaction is the correct one: Donald Trump is a very poor general election candidate and a massive underdog to win the keys to the White House.

A qualification should be noted at the outset. It would be wrong to say that Trump is “unelectable.” Given the partisan configuration of the country, it is possible for any major party candidate to win. Both parties start out with enough safe states that they can win under the right conditions. It’s also worth noting that Hillary Clinton’s high unfavorable ratings suggest that she is a weaker candidate than Barack Obama. Against a generic Republican candidate, she could well be at a disadvantage.

So it’s not literally impossible for Trump to win. Still, it would be a big upset—maybe not Leicester City winning the Premier League big, but big.

Barring economic catastrophe, a poor candidate for the Republicans is like handing an anvil to a mountain climber; they can’t really afford even a modest negative impact.

The fundamental problem for the Republicans is that they’re already at a structural disadvantage in the Electoral College. The last six presidential elections have resulted in four very comfortable Democratic victories, a virtual tie resolved by the Supreme Court, and a narrow win by a wartime Republican incumbent in a decent economy—and George W. Bush was still less than 200,000 votes in Ohio away from a loss. The higher turnouts of presidential elections work against the GOP, and changing demographics are only making the problem worse. Barring economic catastrophe, a poor candidate for the Republicans is like handing an anvil to a mountain climber; they can’t really afford even a modest negative impact.

And the negative effects of Trump might be more than modest. We can start with the fact that outside his core of supporters virtually nobody likes him. Hillary Clinton is given a “very unfavorable” rating by upwards of 40 percent of voters, easily breaking the previous record of a major party nominee set by Bush in 2004. But Trump blows that out of the water; he is viewed very unfavorably by a majority of voters. Admittedly, his unfavorable rating should come down as Republican-leaning voters who didn’t vote for him in the primary start to come around. But the same will be true of Sanders-supporting Democrats when they begin to consider the prospect of a Trump inauguration. Clinton will also have a major asset in appealing to unenthused Democrats—an increasingly popular President Obama campaigning on behalf of his former secretary of state. Trump has already gotten a definitive cold shoulder from the last two Republican presidents.