(CNN)Hillary Clinton ally David Brock says he now believes Donald Trump, not Ted Cruz, will be the likely GOP nominee.
"I may have spoken too soon in predicting in December that the Democrats would face Cruz in November," Brock said in an email to CNN. "I now believe the GOP nominee is likely to be Donald Trump."
Brock is the founder and chairman of American Bridge, a well-funded Democratic super PAC that supports Clinton and opposes prospective opponents.
He said American Bridge is "adjusting its program accordingly," meaning it is targeting Trump more forcefully.
"I don't agree with some Dem thinking that Trump would be easy to beat," Brock added. "He's rewritten all the rules and I would expect a tough race with Hillary."
Politico first reported the adjustment earlier on Sunday.
A source told the news outlet that Brock is "leaning on" American Bridge to "step up delivery" of a Trump opposition research book and is "upping the group's budget."