Sheldon Adelson, one of the Republican Party’s most sought-after contributors, is leaning increasingly toward supporting Marco Rubio — and the Florida senator is racing to win the backing of other uncommitted megadonors who have the potential to direct tens of millions of dollars his way and alter the contours of the Republican primary fight.

Last week, during a campaign swing through Las Vegas, Rubio held a meeting in Adelson’s offices at the Venetian Las Vegas, one of a number of five-star luxury casinos the billionaire mogul owns around the world. Adelson, seated at the head of his conference table, heaped praise on Rubio’s performance while he discussed the dynamics of the 2016 race. Those briefed on the meeting described it as short but said it had an air of importance, with the two joined by Rubio’s campaign manager, Terry Sullivan, and a pair of senior Adelson advisers, Rob Goldstein and Patrick Dumont.