Marco Rubio and Donald Trump emerged Friday as the principal antagonists in an all-out brawl for the future of the Republican Party, as establishment opposition to the front-runner’s candidacy started to crumble with a high-profile endorsement by New Jersey Gov. Chris Christie.

During one of the most hectic and consequential days of the campaign, Rubio dramatically escalated his verbal assault of the real estate mogul, branding him a “con artist” attempting to hijack the party, and the senator from Florida attracted a wave of endorsements. Trump responded with name-calling of his own and by touting the support of Christie, who dropped out of the presidential race after a poor showing in New Hampshire.

The row brought into focus the identity crisis gripping the GOP, pitting those eager to embrace the bravado and nativist message of Trump against those who view him as an existential threat who will drive away minorities and moderates. The endorsement by Christie, a former head of the Republican Governors Association, could prompt other establishment Republicans to fall behind the front-runner.