Trump did not let the issue go after Obama released his long-form birth certificate in 2011 (despite plenty of previously available evidence that he was born in Hawaii). He suggested the birth certificate was fake and encouraged efforts to prove it was fake. "Birtherism" ignited Trump's shocking political ascendance. Most of Trump's supporters now believe Obama is a Muslim not born in this country.
This is among the reasons that Trump's numbers among African-Americans are the worst in political history. It also among the reasons that Trump, despite recent tightening in the polls, is still not likely to win. It is true that Trump has cut Hillary Clinton's lead in the RealClearPolitics national average to just 1.5 percent and drawn even or slightly ahead in key swing states including Florida and Ohio. But keep in mind this happened during Clinton's worst stretch of the campaign in which she nearly collapsed at a 9/11 memorial service and failed to disclose her pneumonia diagnosis for nearly three days.
Presumably, Clinton will begin to perform better on the campaign trail — she has in the last couple of days — and she will have three opportunities in the debates to remind people who already don't think Trump is qualified to be president that voting for him would be a tremendous risk. The latest Quinnipiac poll out this week found that 62 percent of Americans believe Clinton is qualified while 61 percent believe Trump is not.
And remember that even if Trump wins Florida, Ohio, North Carolina and one electoral vote in Maine — along with all the safe red states —he would have just 266 of the 270 electoral votes he needs. He would then need to win Michigan, Pennsylvania, New Hampshire, Colorado or Virginia. He trails in all those states.
And in the GOP primaries, Trump got away with having little or no organization. Winning a national election is a very different endeavor. Obama outperformed his poll numbers in 2012 in large part because he turned out a very diverse electorate in key swing states including Florida, Ohio and Colorado. Clinton has a vastly superior ground game and Trump's birtherism is likely to drive his nonwhite numbers even lower.
And Clinton is not likely to let Trump forget his birther history. She ripped into him on Friday before an African-American audience in D.C. "We know who Donald is. For five years, he has led the birther movement to de-legitimize our first black president," she said. "His campaign was founded on this outrageous lie. There is no erasing it in history."
Clinton then demanded an apology. "Barack Obama was born in America, plain and simple. And Donald Trump owes him and the American people an apology," she said.
Trump will never apologize. He is physically incapable of doing so. And Clinton will skewer him with it and the debates. And the remaining wavering suburban and highly educated Republicans who are now flirting with Trump will be reminded where he came from and what he believes.
—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.