As Republican voters came home, the presidential race was already tightening. But Friday’s bombshell—that the FBI reopened its investigation of Hillary Clinton’s email—has guaranteed a barn-burning end to this extraordinary campaign. Donald Trump’s supporters are enthused, Hillary Clinton’s dispirited. So what to look for on election night?
While votes are still being cast, the TV networks will comment on exit polls, though they won’t reveal what the surveys show about the head-to-head matchup. The exits can be spectacularly wrong—they predicted a John Kerry victory in 2004—but they do influence the coverage. What you see may not be final. Throughout the evening and afterward the poll’s internal numbers are adjusted to match the actual vote.
Two things to look for in the exits: First, how is Mr. Trump doing among white voters? His strategy requires grabbing a higher percentage of whites than Mitt Romney’s 59% and boosting their share of the turnout above 2012’s 72%. College-educated whites traditionally vote Republican, but Mr. Trump has struggled with them. Will he match Mr. Romney’s 51% among all college grads?
Second, how is Mrs. Clinton doing among minorities and millennials? Her strategy calls for replicating President Obama’s 2012 coalition. That year African-Americans were 13% of turnout, and 93% went for Mr. Obama; Hispanics were 10% of turnout, and 71% voted for him; and millennials were 19% of turnout, 60% of whom supported the president.
Actual votes will be reported beginning at 6 p.m., Eastern Standard Time, when polls in parts of Indiana and Kentucky close. At 7 p.m. voting wraps up in Florida (except for the Panhandle), Virginia and western Indiana and Kentucky. Half an hour later, North Carolina and Ohio come in.
These early results could provide important clues about the election’s direction. Watch for how each party’s vote has shifted since 2012. Although Mr. Trump is likely to win Indiana and Kentucky, comparing his margin to Mr. Romney’s might indicate what’s happening nationally.
The second clue will be changes in turnout. Is it larger or smaller than 2012? What about in counties with high percentages of African-Americans, Latinos, millennials and educated whites? These trends will be especially important in the four swing states that report early.
Florida is this election’s most important battleground. Democrats have carried 18 states and the District of Columbia in all of the past six presidential contests. If Mrs. Clinton wins the 242 electoral votes from this “Blue Wall,” she needs only Florida’s 29 to take the White House. Mr. Trump must win Florida to keep open his path to the presidency. Results from early and absentee voting could be an important indicator. The Panhandle, which is very Republican, is in the Central Time Zone, keeping the Sunshine State from being called until late in the evening.
Ohio, with 18 electoral votes, is this year’s second-most important state. No Republican has ever won the White House without the Buckeye State. The split there is big cities versus suburban and rural counties. Mrs. Clinton needs to carry Cuyahoga County (Cleveland) by at least 160,000 votes and win big in Franklin County (Columbus) and Hamilton County (Cincinnati).
The next most important states are North Carolina and Virginia, with a combined 28 electoral votes. Mrs. Clinton can win the presidency by taking the Blue Wall plus these two, even if Mr. Trump wins Florida and every other tossup.
The early returns also include a few bellwether counties. Vigo County, Ind., has backed every presidential winner since 1956 and been wrong only twice since 1888. In Ohio, Ottawa and Wood counties, near Toledo, have voted for every victor since 1964 and 1976, respectively. Hillsborough County, Fla., which includes Tampa, has supported the winner in 19 of the last 20 elections (1992 being the exception).
At 8 p.m., EST, polls close in Florida’s Panhandle, New Hampshire, Pennsylvania, and most of Michigan. An hour later come Arizona, Colorado, New Mexico, Wisconsin and the rest of Michigan’s Upper Peninsula. The Clinton campaign wants Arizona. Mr. Trump needs at least a couple of the other states to get to 270.
At 10 p.m., EST, polls in Nevada and Utah close. The former is a battleground and the latter interesting because of Mormon antipathy for Mr. Trump. Hawaii votes until 11 p.m., EST, and Alaska until 1 a.m. Wednesday. But by then, Americans will probably know the outcome of this strangest of elections. Happy viewing!
Mr. Rove helped organize the political-action committee American Crossroads and is the author of “The Triumph of William McKinley” (Simon & Schuster, 2015).