For those of you who are reading this column after Sunday night, the first and largest uncertainty will be partially resolved: Will Donald Trump put in a debate performance that makes him competitive with Hillary Clinton, as he was before the Sept. 26 debate?
Trump has boasted that he doesn't bother with debate prep, but surely someone who has his attention has pointed out that it's not to his advantage to respond to Clinton's goads like an out-of-control bull. He might have taken the same lesson from watching Mike Pence deflecting Tim Kaine's jabs or from reviewing the first 20 minutes of his own performance Sept. 26.
There are plenty of targets for Trump attacks. Clinton has promised to extend both of President Barack Obama's historic policy initiatives (as described by the millennial generation's Henry Kissinger, his aide Ben Rhodes), Obamacare and the Iranian nuclear deal. Neither is popular.
Last week in Michigan Bill Clinton, more interested than Obama and his wife in how policy works on the ground, noted that under Obamacare, people "wind up with their premiums doubled and their coverage cut in half. It's the craziest thing in the world." Even The New York Times has run a story admitting that Obamacare is foundering and needs major revision.
As for the Iranian nuclear deal, Trump can repeat his previous denunciations. He might also suggest how he would replace the Obama-Kerry groveling diplomacy to Vladimir Putin with using American leverage to outmaneuver a skillful but (he should concede) malign adversary.
If Trump were not to improve in debates, much uncertainty would be leached out of the campaign. Current polling shows him trailing nationally and in target states by margins ranging from large to perceptible. Straight-line extrapolation produces an electoral vote margin much like 2012's 332-206 in favor of the Democrats.
There would remain questions about whether Republicans could run far enough ahead of him to hold their majorities in the Senate (quite possibly) and the House (very likely). But you probably wouldn't have to stay up late on election night to see who's elected president.
It'd be another thing if Trump were to do well in the debates or if Clinton were to crumple or come across as annoying as Kaine.
One reason is that in a race that's close to even nationally, Trump might have an advantage in the Electoral College. Obama carried 115 of 130 electoral votes in the 10 2012 target states; if there are shifts, Democrats have more to lose than Republicans. And as David Byler of RealClearPolitics points out, Trump's appeal, insofar as it's different from that of previous Republicans, means that he's trading votes in safe Republican states for votes in target states.
His weakness among college graduates in such places as north Dallas and west Houston threatens to cut Republican margins in states such as Texas. But his potential strength -- visible in pre-first debate polls -- among non-college-educated whites could provide decisive votes in states with older blue-collar whites, such as Ohio, Iowa, Wisconsin and Nevada, maybe even in Pennsylvania and Michigan.
Another uncertainty is something pollsters can't accurately project: turnout. Reassembling Obama's 51 percent coalition requires robust turnout among blacks, Hispanics and young people. Their turnout has been low in off-year elections, and turnout generally, after rising in the Bush years, has been falling since 2008.
Blacks are unlikely to provide Clinton with as much support as they did the first black president, and polls have found Hispanics less interested in the campaign than whites or blacks.
Young people are a special problem for Clinton, who seems to repel them. Washington Post reporter James Hohmann tracked a young Clinton staffer canvassing around the 65,000-student Ohio State campus. In two hours, the number of people he got to register or sign a card committing to vote: zero. Clinton's organizational edge -- 57 offices, 300 paid staff in Ohio alone -- may not prove cost-effective.
The enormous edge in television advertising she's had heretofore may not, either. In The Weekly Standard, Jeffrey Anderson pointed to evidence that when Trump has reduced Clinton's TV spending advantage, he's done better in polls -- and he has been raising enough money to reduce her edge in the weeks left to go.
Odds clearly favor Clinton. But if Trump can figure out how not to flub debates, uncertainty will increase.