Tough on China policies are the most important issue.

NEW YORK -- Both Democratic and Republican U.S. Senate candidates are increasing their criticism of China, at times using Beijing to attack opponents, as a core part of this year's campaign for control of the legislative chamber.

American voters pick members of Congress alongside the president in November. Democrats and Democratic-leaning independents hold a narrow 51-49 majority in the Senate, but Republicans could retake control of the upper house with a net gain of two seats among the 34 that will be contested this year.

Sharp attacks on China have reached a crescendo in Senate campaigns, pinning the blame on Beijing for a wide range of issues from the fentanyl crisis to the loss of American manufacturing jobs.

Though foreign policy is an uncommon issue in Senate campaigns, being tough on China has become a common stance in both parties as President Joe Biden and Republican presidential nominee Donald Trump have implemented higher tariffs on Chinese goods and strict export controls.

Senate candidates have followed suit, looking to outdo each other in criticizing the world's second-largest economy and portraying it as a threat to American interests.

Most recently, Pennsylvania Republican Dave McCormick defended himself against allegations by Democrats that in his former job as CEO of asset management firm Bridgewater Associates, he helped fund China's largest fentanyl producer.

"As the CEO of a large investment firm, we invested 3% of our -- it was a global firm -- 3% of our portfolio in China," the candidate said. "Most Americans have 30% of the products in their house manufactured in China. So I've laid out a vision for decoupling from China to make sure we're not dependent on China for things like pharmaceuticals and semiconductors."

In Ohio, Democratic incumbent Sherrod Brown in January underscored the urgency for "a China policy for the world we live in today, and we must prepare for what could come tomorrow." The senator has been vocal on the need for policies that stop China from "cheating" and protect American jobs.

Brown's Republican challenger, Bernie Moreno, also described China as an adversary that threatens American workers. But the former car dealer has been attacked by his opponent for selling Chinese-made sport utility vehicles, contradicting Moreno's claims that he refused to sell cars made in China.

"You couldn't trust him as a car dealer, so why would you trust him as your senator?" the narrator said in the ad.

Sen. Jon Tester of Montana, a Democrat running for reelection, described China in a political ad as "the greatest threat facing our nation." Republican challenger Tim Sheehy, meanwhile, warns in a series of television ads that China is building a world-class military and vows to take tough action on Chinese corporations that "rip us off."

Montana Democrats have attacked Sheehy for previously endorsing Chinese drone company DJI and petitioning the Federal Aviation Administration for an exemption allowing his firefighting company to use drones by DJI.

Analysts say congressional attention on Beijing has increased in the past five years in line with the surge in China-related legislation.

Christopher Chivvis and Hannah Miller of the Carnegie Endowment for International Peace wrote that by taking a hard line on China, Republicans look to showcase their fighting spirit and tough-mindedness while Democrats aim to facilitate the passage of policies to improve society and the environment.

"The problem is that these domestic incentives for a more oppositional relationship add to the natural tendency in foreign policy to overestimate the hostile intentions of other powers," they wrote. "Thus, Congress may opt for hard-line policies, even at times when conciliation might be a better approach."

Kyle Jaros, who has researched extensively on how U.S. states have been confronting the perceived "China threat," said there are "political incentives" to be tough on China but that states have differing approaches. He highlighted California as a place where "no Senate candidate, at least on the Democratic side, would hesitate to go after China aggressively as a way to win."