EXCLUSIVE: Sen. Tom Cotton in his Thursday Republican National Convention (RNC) speech will lambaste Democratic presidential nominee Joe Biden and his record on China, a Cotton political adviser told Fox News.

Cotton, R-Ark., was selected to speak on the topic Thursday -- the final and highest-profile day of the convention -- partially because he was one of the earliest elected officials to warn about the coronavirus, which originated in China. Biden's campaign has made a point of emphasizing President Trump's coronavirus missteps and saying that the former vice president would have handled it more effectively. Cotton's speech is apparently set to counter that narrative.

Cotton will "crush Biden on China," the adviser said, previewing the comments. The adviser added that the comments will be tough on Biden's record not only on China but also ISIS, Iran, China and Israel.

In this May 5, 2020, file photo Sen. Tom Cotton, R-Ark., speaks during a Senate Intelligence Committee nomination hearing for Rep. John Ratcliffe, R-Texas, on Capitol Hill in Washington. Cotton will speak at the RNC Thursday. (AP Photo/Andrew Harnik, Pool, File)

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There has been a longstanding rift between Cotton and Biden, dating back at least since Cotton sent a letter signed by himself and 46 other Republican senators to Iranian leaders saying that if they made a deal with the Obama administration that was not satisfactory to GOP senators, a Republican president could leave the deal with no need for congressional approval.

"[W]e will consider any agreement regarding your nuclear-weapons program that is not approved by Congress as nothing more than an executive agreement between President Obama and Ayatollah Khamenei," the letter read. "The next president could revoke such an executive agreement with the stroke of a pen and future Congresses could modify the terms fo the agreement at any time."

Biden shot back that the letter "is beneath the dignity of an institution I revere" and "ignores two centuries of precedent and threatens to undermine the ability of any future American President, whether Democrat or Republican, to negotiate with other nations on behalf of the United States."

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Cotton responded: "It's a simple fact of our Constitution that if Congress does not approve that deal, then it may not last."

On the coronavirus, Cotton was accused of spreading conspiracy theories in February when he suggested that instead of coming from a wet market, the virus may have escaped from a lab near the Wuhan market initially thought to be where the virus first jumped from animals to humans. Fox News reported in April that multiple sources who had been briefed on the details of early actions by China's government and seen relevant materials had increasing confidence that the virus may have escaped from a Wuhan laboratory, where a naturally occurring strain was apparently being studied -- not as a bioweapon but as part of China's attempt to demonstrate its efforts to identify and combat viruses are equal to or greater than the capabilities of the United States.

Still, no public evidence has yet been presented to definitively point to the lab scenario, and Defense sources who have spoken to Fox News said earlier this year it was being viewed as simply one of two theories about how the outbreak began.

The senator, in his speech focusing on foreign policy, will also use the words of a former Obama official against Biden.

Democratic presidential candidate former Vice President Joe Biden speaks during the fourth day of the Democratic National Convention, Thursday, Aug. 20, 2020, at the Chase Center in Wilmington, Del. (AP Photo/Andrew Harnik)

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"Barack Obama's own secretary of Defense said Biden was wrong on every foreign policy issue," the Cotton political adviser said.

Former Obama Secretary of Defense Robert Gates previously said Biden was "wrong on nearly every major foreign policy and national security issue over the past four decades" and doubled down on that statement in an interview with CBS' "Face the Nation" last year.

The Cotton political adviser also said the Cotton speech would not just address Biden's policy stances during the Obama administration but would also touch on "Biden's 50-year record" as a senator.

Biden surrogates, however, have slammed Trump on his foreign policy history, which was a topic at the Democratic National Convention last week. Former Secretary of State John Kerry, who like Biden served in the Obama administration, provided some of the most high-profile jabs on the topic.

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“When this president goes overseas, it isn’t a goodwill mission it’s a blooper real,” Kerry said Tuesday night. “He breaks up with our allies and writes love letters to dictators. America deserves a president who's looked up to, not laughed at."

Biden, in his own convention speech, called Trump "a president who takes no responsibility, refuses to lead, blames others, cozies up to dictators, and fans the flames of hate and division."

Cotton has been floated as a potential 2024 presidential candidate and is considered to be one of the Republicans to carry on the banner of Trump-style Republicanism after the president leaves office, whether that's this coming January or in 2025.

Fox News' Caitlin McFall, Bret Baier and Gregg Re contributed to this report.