New Jersey Sen. Cory Booker, struggling for months to gain traction in his presidential campaign, looked for an opening at Wednesday night’s Democratic debate by criticizing rival Elizabeth Warren’s signature policy proposal for a wealth tax on the country’s wealthiest.

Warren touted the wealth tax — 2 cents on the dollar for fortunes greater than $50 million — saying it could pay for universal child care, free college, and more.

“A two-cent wealth tax and we can invest in an entire generation’s future,” Warren said.

Booker split from Warren, one of the front-runners for the Democratic nomination to take on President Donald Trump. Booker said that while he agrees with the need to do “all of those things," the wealth tax isn’t the way to do them.

“But the tax the way you’re putting it forward, I’m sorry, it’s cumbersome," Booker said. It’s been tried by other nations.”

“If we as a party don’t start talking not just about how to tax wealth,” Booker said, “but how to give more people opportunities to create wealth, to grow businesses, to have their American dream — because yeah we need to raise the minimum wage, but the people in communities I frequent, their aspiration for their lives is not just to have those fair wages, they want to have an economy that provides not just equalities in wealth, but they want to have equalities in opportunity.”

Warren shot back later: I’m tired of free-loading billionaires.

Booker has struggled to establish himself as an alternative to Joe Biden for moderates, and for well-heeled donors, as the former vice president’s campaign has stalled. The political challenge for Booker only intensified recently with the entry of former Massachusetts Gov. Deval Patrick into the race, as well as the possible candidacy for former Mayor Michael Bloomberg. Both candidates could conceivably compete for support among moderate Democrats.