He would begin that matchup at a significant disadvantage.
Yes, it’s still a long way until Election Day. And Mr. Trump has already upended the conventional wisdom many times. But this is when early horse-race polls start to give a rough sense of the November election, and Mr. Trump trails Mrs. Clinton by around 10 percentage points in early general election surveys, both nationally and in key battleground states.
Could Mr. Trump overtake Mrs. Clinton? Sure. Mrs. Clinton is very unpopular herself. Her polling lead is a snapshot in time, before the barrage of attack ads that are sure to come her way. There have been 10-point shifts over the general election season before, even if it’s uncommon. But there isn’t much of a precedent for huge swings in races with candidates as well known as Mr. Trump and Mrs. Clinton. A majority of Americans may not like her, but they say they’re scared of him. To have a chance, he’ll need to change that.
Mr. Trump’s biggest problem is that he would be the most unpopular major party nominee in the modern era, with nearly two-thirds saying they have an unfavorable opinion of him. More than half view him “very unfavorably” or say they’re “scared” of his candidacy — figures with no precedent among modern presidential nominees.
Mr. Trump’s ratings are worst with the voters who made up the so-called Obama coalition of young, nonwhite and well-educated voters who propelled President Obama’s re-election four years ago.
In some ways, Mrs. Clinton is not a natural fit to reunite Mr. Obama’s supporters — especially the younger voters who have overwhelmingly preferred Senator Bernie Sanders in the Democratic primaries. But whatever challenges she may have among these groups dissipate against Mr. Trump. Recent surveys even show her leading among 18- to 29-year-old voters by a larger margin than Mr. Obama’s when he won them four years ago.
Mrs. Clinton’s strength among young, nonwhite and well-educated voters would be enough to make her a favorite. The G.O.P. path to victory without adding some of these voters is narrow. The Republicans would need to do nearly as well among white voters as Ronald Reagan did in his 18-point re-election landslide in 1984 merely to fight to a draw in today’s far more diverse country. Nonwhite voters could make up nearly 30 percent of the electorate in 2016, up from 14 percent in 1984.
But what raises the possibility of a more decisive defeat for Mr. Trump is that he is struggling to reunite the voters who supported Mr. Romney — especially white women and white college-educated voters.
A recent ABC/Washington Post pollshowed Mr. Trump with just a 29 percent favorability rating among white women and 23 percent among white college graduates, while 68 percent and 74 percent had an unfavorable opinion.
Mr. Trump is faring worse than Mr. Romney among white voters in all of the presidential battleground states. Polls even show Mr. Trump losing white voters in states where Mr. Romney won them, like Colorado,Pennsylvania and Wisconsin. It’s enough to put him at a big disadvantage in early surveys of diverse battleground states like Florida and Virginia — as well as North Carolina and Arizona, two states Mr. Romney won in 2012.
Mr. Trump has even trailed in a poll in strongly Republican Utah, which is one of the best-educated states in the country. It’s unlikely that Mrs. Clinton could win Utah in the end, but it’s nonetheless telling that Mr. Trump trails in a survey of a state where Democrats have not reached 35 percent of the vote in the last 11 presidential elections.
The Trump campaign’s aim to compete in industrial Democratic-leaning states like Pennsylvania, Michigan and Ohio has not looked promising either. That’s in part because of his broader challenge with well-educated whites (a recent NBC/Marist survey showed Mr. Trump trailing by 29 points in the Philadelphia suburbs), but it’s also because he isn’t connecting among white working-class Democrats the way the campaign had hoped.
The same NBC/Marist survey showed Mrs. Clinton leading in western Pennsylvania, where Mr. Obama lost many registered Democrats to Mr. Romney.
Part of the problem for Mr. Trump is that the anger that has driven his success in the Republican primaries isn’t seen at the same levels in the general electorate.
A majority of Americans now narrowly approve of Mr. Obama’s performance — a big improvement from his standing in surveys ahead of the midterm elections, when his ratings were decidedly negative. An ABC/Washington Post poll found that just 24 percent of Americans were angry at the federal government.
There also isn’t much evidence that Americans are particularly dissatisfied with the state of the economy. The unemployment rate is at 5 percent, and gas prices are low. Consumer and economic confidence indicators are well within historical norms.
By all of these measures, national political and economic conditions are more favorable to the president’s party than they were at this time in 2012, when Mr. Obama won re-election. These indicators might make Mrs. Clinton a slight favorite even if she were facing a more typical Republican nominee. Instead, it seems she will be facing a nominee who has both defied expectations and created enormous challenges for himself.