And it is difficult to see Trump outperforming Romney in any demographic group except noncollege educated white males. Trump now leads Clinton among this group by 69-27 percent, according to the ABC/Washington Post poll, ahead of Romney's 64-33 percent win total in 2012. But there is a big problem with Trump's white support. It falls off a cliff with college-educated whites, who are more likely to vote.
Among white voters with a college degree, the race is essentially tied, 43-42 percent in favor of Clinton. Romney won this group by 14 points in 2012.
And Trump's performance among non-white voters is abysmal. In the NBC/WSJ poll, just 14 percent of Hispanic voters say they will support Trump and 82 percent say they view him unfavorably. This will hurt Trump in swing states including Florida and Colorado.
Among black voters, Quinnipiac recently had Trump at 1 percent. In recent polling in Ohio and Pennsylvania, Trump had zero percent black support. Literally none. According to the Cook Political Report, black voters provided Obama's winning margin in Pennsylvania, Ohio, Florida, Maryland, Michigan, Nevada and Virginia.
To attempt to soften Americans' views of him, Trump in Cleveland will rely in large part on members of his own family. On Monday night, Trump's wife, Melania, will address the nation in prime time. On Tuesday it will be his children Tiffany and Donald Jr. and on Wednesday Eric Trump will speak. To round things out on Thursday, Ivanka Trump will introduce her father for his acceptance speech.
These family members could very well help improve Trump's image, especially among white women, where he is now essentially tied with Clinton. Romney won white women by 14 percent.
But look elsewhere in the Cleveland speakers list and you will find many conservative white men speaking who are unlikely to boost Trump among demographic groups where he needs to perform much better to have any chance of winning. Monday night's speakers include Willie Robertson of "Duck Dynasty," Texas Gov. Rick Perry, Sens. Tom Cotton and Jeff Sessions and New York Mayor Rudy Giuliani.
These speakers will likely thrill Trump's base but do little to broaden his appeal. The following nights run along similar lines, though there are several women speakers and at least a few minorities.
But if Trump comes out of Cleveland with a poll bounce that is mainly driven by increased enthusiasm among noncollege educated whites, he will have achieved very little. And that bounce will almost certainly get wiped out by Clinton's convention in Philadelphia, which will include addresses from Sens. Bernie Sanders and Elizabeth Warren and Obama, whose approval ratings now routinely top 50 percent.
The general election polls that really matter will emerge in August, after the convention bounces fade and the race settles ahead of the debates. If Clinton is still close to Trump among white women and college-educated whites overall, the outcome in November is not likely to be close. Because she is going to run up the score among minority voters in possibly historic ways.
—Ben White is Politico's chief economic correspondent and a CNBC contributor. He also authors the daily tip sheet Politico Morning Money [politico.com/morningmoney]. Follow him on Twitter @morningmoneyben.