And as people like Mitt Romney have said they can't support Trump, the question of whether the other Republican candidates would support Trump as nominee and break the pledge they signed has come up — including on Tuesday.
Asked during the debate, Marco Rubio said he would support Trump if he is the Republican nominee.
The full exchange:
BRET BAIER: In 30 seconds, can you definitively say you will support the Republican nominee even if that nominee is Donald J. Trump? Sen. Rubio, yes or no?
MARCO RUBIO: I'll support the Republican nominee. I'll support Donald if he's the Republican nominee and let me tell you why: Because the Democrats have two people left in the race; one of them is a socialist. America doesn't want to be a socialist country — if you want to live in a socialist country, then move to a socialist country. The other one is under FBI investigation, and not only is she under FBI investigation, she lied to the families of the victims of Benghazi. And anyone who lies to the families of the victims of the people who lost their lives in the service of their country, can never be the commander in chief of the United States. We must defeat Hillary Clinton.