As I've watched many inquiries open over the last couple of days about the feasibility of replacing Donald Trump as the Republican presidential candidate at this late date, it's worth discussing important distinctions between what can and what cannot be done at this date; and if things can be done, why, as a practical matter, they will not work. There is really only on option available--Donald Trump dropping out, naming a new candidate, communicating that to voters, and relying on the Electoral College.
It is too late for Donald Trump's name to be taken off the printed ballot. This should be obvious. We're in a period of early voting, absentee voting, voting overseas, and simply the act of printing ballots.
It is practically too late to replace Mr. Trump without his consent. While there are some rather fantastic hypotheticals ranging from the Republican National Committee replacing him under Rule 9 to instructing presidential electors to vote for someone else, this is, as a practical matter, impossible.
For starters, the notion of the RNC replacing him was driven by hopes to change the words printed on the ballot months ago. If he's on the ballot, running as the candidate, then the RNC's 11th hour decision to replace him would go nowhere. A second rogue candidate roaming the country as Trump insists he's still the nominee, still printed on the ballot? Quite a challenge.
Additionally, even if the RNC convinced the public that a new nominee was the real nominee, and perhaps hoped the Electoral College would solve the problem, it's too late as a practical matter on that front, too. For starters, Trump would be demanding electors vote for him, too, causing deep confusing in the public and a high unlikelihood that the hybrid form of the Republican ticket secured 270 electoral votes.
Also, electors were selected months ago. I floated the notion back then of the "Trojan Electoral College," where state parties are usually in charge of selecting electors. If these parties unified to select electors committed to a Romney-Pence or Pence-Kasich ticket, they could have done so with some ease (subject to a few likely-unconstitutional laws that purport to legally bind presidential electors to the nominee).
But that ship has sailed. It's like pulling teeth to secure the lists of presidential electors in some places. In Illinois, it includes a few loyal to Ted Cruz, Marco Rubio, and John Kasich. In that state, however, it's unlikely to matter, of course. But Mr. Trump has had a significant imprint on the slates of electors elsewhere. Consider Ohio, where one such elector is Kathy Miller, who was heading up Mr. Trump's efforts in a part of the state (at least, until a recent gaffe involving racially-charged remarks forced her resignation).
Even if one could convince the public that casting votes for Mr. Trump on the ballot would leave the decision to the Electoral College, these electors include some who are fiercely loyal to Mr. Trump. In the event he does not drop out, they are unlikely to vote for anyone else but Mr. Trump.
(UPDATE: As a point of clarification, it would be legally and constitutionally permissible for Republicans to pursue this route, as Professor Ned Foley has thoughtfully explained. I simply believe it's deeply impractical and work from that assumption.)
It is not too late for Mr. Trump to drop out, for the party to name a new slate, for voters to understand that, and for the Electoral College to vote for a new slate. Because of all these problems, the first, and biggest, step is for Mr. Trump to drop out. After that, everything else falls fairly naturally into place.
First, the RNC could easily (and fairly informally) name a new ticket, of "Romney-Pence" or "Pence-Kasich" or whatever it may be. Yes, the ballots would still read "Trump-Pence," but, like, say, Mel Carnahan 2000, voters would know (quite quickly!) that these words are simply hieroglyphics that mean an entirely different ticket.
Assuming that works for Republicans and it appears they've secured enough electoral votes after November 8, the Electoral College meets December 19 and votes. While many states require electors to pledge to support candidates, only a few purport to make those pledges binding. And they're probably unconstitutional. Electors could gather and vote for the new ticket with little difficulty. In the few states with binding laws, I imagine state attorneys general or secretaries of state would not attempt to enforce such laws--but there's certainly a litigation risk. But consider that it would be an attempt to force electors to vote for a man who'd already dropped out of the race! Curious result indeed.
There are further complications that could arise, but this scenario would be a fairly straightforward and easy to do. It's triggered by a voluntary decision by Mr. Trump, of course, which is the biggest problem. But when many call upon Mr. Trump to drop out, it's worth noting that this is the scenario that would unfold if he did.