The United States needs to be tough on China during trade negotiations — but the way President Donald Trump is going about it is worrying, Sen. Richard Blumenthal, D-Conn., told CNBC on Thursday.

Trump on Thursday called tariffs an "excellent" alternative to a trade deal, hours before Chinese officials were set to meet U.S. trade negotiators in Washington.

"The kind of gamesmanship that we're playing right now really worries me. I don't see the end game here in terms of the tit-for-tat the president is playing with the Chinese," Blumenthal, who sits on the Judiciary Committee, said on "Squawk Alley."

On Sunday, Trump announced that U.S. tariffs on $200 billion worth of Chinese goods would jump to 25% because the Chinese were attempting to renegotiate terms of the deal. The increase is set to kick in at 12:01 a.m. ET Friday.

However, the president has suggested the administration may reverse the decision, depending on how negotiations go. China's Vice Premier Liu He is set to dine with Trump's trade team Thursday evening, just a few hours before the deadline.

"It's possible to do it; they're all here," Trump told reporters at the White House on Thursday.

However, he also said, "Our alternative is an excellent one."

"It's an alternative I've spoken about for years. We'll take in well over a hundred billion dollars a year. We never took in 10 cents from China," Trump said, referring to additional tariffs he promised to impose on China. "And I think it'll be a very strong day, frankly. But we'll see."

On Wednesday night, Trump said that China "broke the deal." Those remarks sent the market plunging on Thursday, but stocks cut their losses later in the day after the president said a trade deal is still possible.

Blumenthal called the escalating tariff threats "a game of chicken."

He said, however, there are pressing issues that need to be dealt with, such as the allegations of intellectual property theft and China's currency manipulation.

"I support certainly driving a hard bargain and insisting on fair treatment for our intellectual property, for our currency, for our products sold abroad," he said. "We need to insist on a hard line."

— CNBC's Kevin Breuninger contributed to this report.