Recount battles in Michigan, Wisconsin and Pennsylvania are not expected to yield an Electoral College victory for Hillary Clinton. That leaves one last-ditch opportunity to bar Donald Trump from the White House: the Electoral College vote on Dec. 19, when 538 electors will gather in their respective states to choose the president. On Monday, Christopher Suprun, an elector from Texas, became the first Republican to say publicly that he won’t vote for Mr. Trump, who won his state. Mr. Suprun mentioned Gov. John Kasich of Ohio as a Republican he could support. But on Tuesday, Mr. Kasich said he wasn’t interested.

Republican insiders say there are more “faithless electors” like Mr. Suprun out there, quietly plotting to dump Mr. Trump. Here are four things to remember about their scheme.

1. It’s a moon shot. Electors are typically chosen by their state’s party leaders. In most states they’re legally bound to vote for their party’s nominee, but such laws haven’t been enforced and it’s accepted that electors can vote their consciences. Still, in our nation’s history, 99 percent of electors have stuck by the nominee. For Donald Trump to fall short of the 270 electoral votes he needs to take office, 37 electors would have to abandon their pledge to him. If neither he nor Mrs. Clinton reaches 270, that would throw the election to Congress, where …

2. Republicans control the House. The House would vote for the president from among the three top electoral vote-getters, which in this case would be Mr. Trump, Mrs. Clinton and any third person chosen by the greatest number of faithless electors. By law, that third person needn’t be a declared presidential candidate: He or she can be any American who meets the qualifications to serve. Each state delegation in the House casts one vote. And since House Republicans are inclined to vote for Mr. Trump …