But the results so far also indicate he could still be defeated, suggesting Mr. Trump is far from winning a majority of the popular vote. He could be denied a majority of delegates if the field narrowed to Mr. Rubio.

If the remaining states vote as one would expect based on their demographics and the results so far, Mr. Trump will defeat Marco Rubio by a margin of 37 percent to 25 percent over the rest of the race. Ted Cruz would take third place over the rest of the primary season, with 22 percent of the vote. (These figures were calculated by weighting the candidate’s projected vote share in congressional districts by Mitt Romney’s vote in 2012, to more appropriately reflect the importance of caucuses. The actual popular vote would be worse for Mr. Cruz.)

Mr. Trump’s 12-point lead over Mr. Rubio would translate into a huge majority of the outstanding delegates. He would be favored to amass around two-thirds of the delegates that remain — or around 1,100 additional delegates on top of the more than 300 delegates he already holds. That would easily be enough for Mr. Trump to clear the 1,237 delegates needed to win.