Senator Richard Blumenthal said he would open a perjury investigation into the ousted homeland security secretary Kristi Noem after alleging she lied to Congress about the hidden influence her senior adviser Corey Lewandowski had over the agency’s contracts.

Blumenthal, a Connecticut Democrat and ranking member on the Senate’s permanent subcommittee on investigations, said Thursday he would push the panel to look into whether Noem committed perjury at a hearing this week, when she flatly denied Lewandowski had played any role in approving Department of Homeland Security (DHS) spending. Blumenthal said Democrats had evidence to prove otherwise.

“Her firing doesn’t absolve her or relieve her of potential liability for perjury,” he said. “We are going to pursue an investigation of the evidence that she lied, because it relates to corruption in the administration.”

At Tuesday’s hearing, Blumenthal had pressed Noem on whether Lewandowski, a longtime Trump ally serving as her senior adviser, was involved in approving contracts. She described him as a “special government employee” working for the White House, so when Blumenthal characterized that as a contracting role, she said simply: “No.”

The following day, Blumenthal sent her a letter arguing that DHS records told a different story: that Lewandowski had personally signed off on contracts and that staff in the department treated his signature as a green light for spending. “There are criminal penalties for knowingly and willfully making materially false statements or representations to Congress,” he wrote.

Federal procurement records reviewed by the Guardian show that last year, DHS awarded a $250,000 public affairs contract to American Made Media Company, a newly formed Republican political consultancy whose principals have deep professional ties to Lewandowski. The posting, published on 26 September with bids due the very next day, was unusual not only for the tight timeline but for its obviously partisan requirements: the winning firm would need to demonstrate “an established track record of promoting Trump administration policies in the media”. Four days after it went live, the American Made Media Company had the contract.

The company is led by veterans of Trump’s presidential campaigns, several of whom worked directly alongside Lewandowski, who managed Trump’s 2016 campaign, on political and legal efforts tied to the president. The Guardian found no record of prior government contracting work by the firm.

Reporting by Politico last August also described Lewandowski as being involved in clearing six-figure contracts at the Federal Emergency Management Agency (Fema), which is a part of the DHS. The Wall Street Journal later found that contracts above $100,000 had been routed through the secretary’s office, which handed Noem and Lewandowski unusual sway over the department’s spending.

Still, with the Senate under GOP control, Blumenthal cannot compel witnesses or issue subpoenas without the blessing of subcommittee chair Ron Johnson of Wisconsin, who has given no indication he intends to go that route. What Blumenthal can do, however, is hold public forums, demand documents and solicit whistleblowers – tools he made clear he intends to deploy.

Noem was fired after facing bipartisan criticism at a series of congressional hearings, including scrutiny over a $220m border security advertising campaign that prominently featured her image. Noem claimed that Trump had approved of the spending, but Trump flatly rejected her claims, and told Reuters on Thursday he had no knowledge of it.

Noem’s dismissal was perhaps not shocking considering how she had spent months accumulating political damage, and the White House had reportedly been given advance warning that patience was wearing thin.

According to PBS reporter Lisa Desjardins, Republican senator John Kennedy, who probably had stung Noem the hardest in his congressional questioning, told the reporter he had given the White House a heads-up that he had questions about Noem “gnawing at him”, and that he had received information contradicting her account of how millions in advertising money was contracted out to political allies and former associates.

When asked whether someone was not telling the truth about the details behind the spending campaign , Kennedy said: “I’m confident in my information.”