Senator Bernie Sanders is hoping to set himself apart from the rest of the competition — particularly his chief rival in former Vice President Joe Biden — on a signature issue where President Donald Trump also has focused much of his attention: trade.

Biden, who entered the race a week ago, leads Sanders in most polls, and he raised a few eyebrows Wednesday by downplaying the economic threat China poses to the United States, even mocking Beijing at an Iowa campaign stop.

“China is going to eat our lunch? Come on, man,” Biden said.

Sanders is making his case against Biden, highlighting that he’s been against the North American Free Trade Agreement and the Trans-Pacific Partnership trade agreements, and even took a shot at the former vice president on Twitter.

Sanders wasn’t alone in his criticism as even Sen. Mitt Romney, R-Utah, took a shot at Biden in a tweet of his own.

The Biden campaign has yet to respond, but Trump won traditional manufacturing states like Pennsylvania (Biden’s home state), Michigan and Wisconsin in 2016 by promising to get U.S. trade imbalances in check, particularly by cracking down on China.

The Trump administration has slapped tariffs on billions of dollars in Chinese goods, and there are hopes a new trade agreement with China will be reached soon.

Per CNBC:

The president has found kindred spirits on the Democratic side. Primary candidates such as Sanders and Sen. Elizabeth Warren, D-Mass., have argued that free trade agreements have hurt American workers by encouraging companies to hire overseas.

On Monday, Sanders released a trade plan designed to put more pressure on Trump over trade policy. He called on all of his presidential rivals to pledge to renegotiate U.S. trade deals and label China a currency manipulator, among other proposals. Trump promised to label China a currency manipulator but has not yet done so.

Biden — who has pegged his presidential hopes in part on winning his home state of Pennsylvania — will have to defend his trade policy history as he tries to garner support in Midwestern states. As a senator, he voted to ratify NAFTA. As vice president, he also pushed for the TPP agreement — which Trump, Sanders and several Democratic senators running for president opposed.

On Monday, Sanders drew a distinction between himself and the former vice president on trade.

“I helped lead the fight against NAFTA. He voted for NAFTA,” he told CNN. “I helped lead the fight against (normal trade relations) with China. He voted for it. I strongly opposed the Trans-Pacific Partnership. He supported it.”

While Biden did not respond to Sanders’ specific criticism, he defended his policy history Tuesday.

“I’m proud of my record,” he said in Iowa.

Most early polls have showed Biden and Sanders leading the Democratic primary field nationally.