U.S. Rep. Chrissy Houlahan on Monday said that if President Donald Trump used foreign aid as leverage to coerce Ukraine into investigating Joe Biden, she would consider that an impeachable offense.

Unlike many House Democrats, Houlahan, a freshman representative from Chester County, has resisted calls from the left to initiate impeachment proceedings in the aftermath of Special Counsel Robert Mueller’s investigation into Russian interference in the 2016 election and whether the Trump campaign cooperated in that.

But in a sign that the politics around impeachment may be shifting, Houlahan on Monday wrote a joint opinion article in the Washington Post with other moderate Democrats saying that the latest allegations against Trump were “stunning, both in the national security threat they pose and the potential corruption they represent.”

“This flagrant disregard for the law cannot stand. To uphold and defend our Constitution, Congress must determine whether the president was indeed willing to use his power and withhold security assistance funds to persuade a foreign country to assist him in an upcoming election,” Houlahan wrote with six fellow Democrats.

“If these allegations are true, we believe these actions represent an impeachable offense. We do not arrive at this conclusion lightly, and we call on our colleagues in Congress to consider the use of all congressional authorities available to us, including the power of 'inherent contempt’ and impeachment hearings, to address these new allegations, find the truth and protect our national security.”

In an interview Tuesday, Houlahan said her potential support for impeachment hearings did not stem from a culmination of concerns about Trump or a “straw that broke the camel’s back.”

“I think that it is a particular situation that has been identified by our intelligence community of being worthy of finding out more information and being of an urgent nature,” she said. “This is a combination of all kinds of worries. It’s a national security concern on a very high level. It’s also a really high-level concern of corruption at the highest level of our government.”

The article came amid a clash between the Democratic-controlled House and the executive branch over a whistle-blower complaint filed by a member of the intelligence community, reportedly involving a promise Trump made to a foreign leader. The Wall Street Journal reported last week that in a July phone call, Trump repeatedly pressured Ukraine’s president, Volodymyr Zelensky, to investigate Biden.

Democrats are investigating whether the White House had withheld hundreds of millions of dollars in aid to Ukraine to pressure the country to probe the former vice president and his son Hunter’s business dealings there.

Houlahan said in a statement accompanying release of the op-ed Monday night that if the Trump administration continues to refuse to comply with congressional demands for information like the complaint and a transcript of the president’s phone call, she would call for a formal authorization of an impeachment investigation.

The director of national intelligence, Joseph Maguire, has thus far refused to provide the whistle-blower complaint to Congress, citing guidance from the Justice Department. He is set to testify on Thursday before House and Senate committees.

“I would assume that’s a pretty big first step about how all of us are going to be approaching this situation,” Houlahan said in the interview.

Trump has acknowledged discussing Biden on the call but denied doing anything improper.

“If we’re supporting a country, we want to make sure that country is honest,” Trump told reporters Monday at the United Nations. “If you don’t talk about corruption, why would you give money to a country that you think is corrupt? One of the reasons the new president got elected is he was going to stop corruption. So it’s very important that on occasion you speak to somebody about corruption. Very important.”

On Tuesday, Trump confirmed he had ordered his administration to halt nearly $400 million in aid to Ukraine, saying he wanted European countries to contribute more to Ukraine’s defense. The Trump administration eventually released the funding, which had been appropriated by Congress, amid scrutiny from the news media and lawmakers.

Joining Houlahan in writing the article were Reps. Gil Cisneros (D., Calif.), Jason Crow (D., Colo.), Elaine Luria (D., Va.) Mikie Sherrill (D., N.J.), Elissa Slotkin (D., Mich.) and Abigail Spanberger (D., Va.). The representatives share national security backgrounds; Houlahan is an Air Force veteran.

Other Philadelphia-area House Democrats, like Reps. Madeleine Dean of Montgomery County and Mary Gay Scanlon of Delaware County, had already announced their support for an impeachment inquiry.

Support from members like Houlahan, who won a Republican-held seat, could increase pressure on Speaker Nancy Pelosi to move toward impeachment proceedings.

Asked whether Democrats might suffer politically if they moved toward impeachment without GOP support, Houlahan said, “This is not a partisan thing. This is a country thing.”