If the nominee withdraws or dies in the second half of October

[President Johnson]

What happens if a presidential candidate either withdraws his or her candidacy or dies in the closing days of the campaign? I mean, the Republican or Democratic National Committees can determine another nominee (probably the vice president), but most if not all ballots have been printed and early voting  begun in some states. Are the votes for the withdrawn candidate counted as votes for the new nominee of this party? If not, the other side would be ensured to win the election, and even if this person only gets less than 45% in a two way race.

[MASHED POTATOES. VOTE!]

Taft's Vice President James S. Sherman died after being renominated on October 30, way too late for being replaced by the party and on the ballot the way Thomas Eagleton was replaced by the DNC. Instead the RNC simply proclaimed that Nicholas Murray Butler should receive any electoral vote Sherman would've been entitled to.

[brucejoel99]

Yes, the popular votes cast for the withdrawn candidate would be counted as votes for the party's new nominee. This is because, on Election Day, voters actually vote for members of the Electoral College (which formally selects the President- & Vice President-elect at the meeting of the Electoral College several weeks later in December) rather than for the presidential or vice presidential nominees whose names are physically printed on ballots nationwide.

If a vacancy happens in either the presidential or vice presidential nomination during the general election campaign, which roughly extends from the party nominating conventions through Election Day in November, then the political parties' committees would follow their long-established rules in providing for replacement(s) by their respective national committees. The electors, who are predominantly party loyalists, would abide by the national party's decisions.

The main precedent that would apply here would be 1912 (as Keyboard Jacobinism pointed out), when Vice President James S. Sherman, President Taft's running mate, died on October 30th, just 6 days before the November 5th general election. The RNC nominated Columbia University President Nicholas M. Butler to replace Sherman, & all 8 GOP electors subsequently voted for Butler. It is (& would be) as simple as that, really.

[Del Tachi]

The withdrawn/dead candidate's name would remain on the ballot in most states, but the electors in those states would probably all get together and vote for a (not dead) candidate when the electoral college convenes in December.