The Kentucky senator Rand Paul promised on Saturday to wage a vigorous review into the origins of the coronavirus if Republicans retake the Senate and he lands a committee chairmanship.

Speaking to supporters at a campaign rally, the senator denounced what he sees as government overreach in response to Covid-19. He applauded a recent judge’s order that voided the federal mask mandate on planes and trains and in travel hubs.

“Last week I was on an airplane for the first time in two years and didn’t have to wear a mask,” he said, drawing cheers. “And you know what I saw in the airport? I saw at least 97% of the other free individuals not wearing masks.”

Paul has clashed repeatedly with Dr Anthony Fauci, the top US infectious disease expert, over government policies and the origins of the virus.

Paul, who is seeking a third term, said he was in line to assume a committee chairmanship if the GOP wins Senate control. The Senate has a 50-50 split, with the vice-president, Kamala Harris, the tie-breaking vote.

“When we take over in November, I will be chairman of a committee and I will have subpoena power,” Paul said. “And we will get to the bottom of where this virus came from.”

The senator, an ophthalmologist before politics, continued to offer his theory about the origins of the virus.

“If you look at the evidence, overwhelmingly, not 100%, but overwhelmingly the evidence points to this virus being a leak from a lab,” Paul said.

Many US conservatives have accused Chinese scientists of developing Covid-19 in a lab and allowing it to leak.

US intelligence agencies remain divided on the origins of the coronavirus but believe China did not know about the virus before the start of the global pandemic, according a Biden-ordered review released last summer.

The scientific consensus remains that the virus most likely migrated from animals. So-called “spillover events” occur in nature and there are at least two coronaviruses that evolved in bats and caused human epidemics, SARS1 and MERS.

At the Kentucky rally, the Senate Republican leader, Mitch McConnell, the state’s senior senator, also pointed to Paul’s opportunity to lead a committee. If that occurs, he said, Paul would become chairman of “one of the most important committees in the Senate – in charge of health, education, labor and pensions”.

McConnell was upbeat about Republican prospects in November.

“I’ve never seen a better environment for us than this year,” said McConnell, who is in line to again become majority leader.

The rally featured other prominent Kentucky Republicans, including several considering running for governor in 2023, when Andy Beshear, a Democrat, will seek a second term.

In his speech, Paul railed against socialism, saying it would encroach on individual liberties. The senator was first elected to the Senate in the Tea Party wave of 2010.

“When President Trump said he wanted to ‘Make America Great Again’, I said, ‘Amen,’” Paul said. “But let’s understand what made America great in the first place, and that’s freedom, constitutionally guaranteed liberty.”

Charles Booker is by far the best known Democrats seeking their party’s nomination for Paul’s seat in the 17 May primary. Paul is being challenged by several little-known candidates. A general election campaign between Paul and Booker would be a battle between candidates with starkly different philosophies.

Booker, a Black former state lawmaker, narrowly lost a bid for the Democratic nomination in 2020. He is a progressive who touts Medicare for all, anti-poverty programs, a clean-energy agenda and criminal justice changes.

Paul, a former presidential candidate, has accumulated a massive fundraising advantage.

Kentucky has not elected a Democrat to the US Senate since Wendell Ford in 1992.