(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.

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