Ryan says he will run for Speaker if Republicans in the House unite behind him. That means his bid for speaker hinges primarily on whether the right-wing Freedom Caucus will support him.
This is important because, for anyone to be elected Speaker of the House, he or she needs to win a majority vote in the entire chamber. And since, in practice, the vote is always partisan, that means that the winning candidate needs to get a huge supermajority of his or her caucus — 88 percent for a Republican candidate this year:
Javier Zarracina / Vox
That means that if the Freedom Caucus’s members voted as a bloc on the floor — and it wasn’t yet clear that they would — they would have had the power to prevent a Republican candidate they don’t like from getting those necessary 218 votes.
So Ryan is telling the recalcitrants, in effect, “Get behind me now — before the floor vote — or I won’t bother running, and good luck with whoever the other candidates turn out to be.”