WASHINGTON — Freshman Rep. Sean Casten, an Illinois Democrat who flipped a suburban Chicago congressional district in 2018, told the Chicago Sun-Times on Wednesday he backs launching an impeachment inquiry into President Donald Trump.

“I am in favor of initiating an impeachment inquiry,” Casten said in an interview in his Cannon House building office.

Casten is among the 44 House Democrats facing the toughest GOP challenges in 2020, according to a “frontline” list compiled by the Democratic Congressional Campaign Committee.

His public call stands out because Casten is only the third in this group of 44 to support an impeachment inquiry. Casten joins freshmen Katie Porter of California and Tom Malinkowski of New Jersey – a friend whose office is down the hall from Casten’s.

Rep. Jan Schakowsky, D-Ill., also on Wednesday called for a Trump impeachment inquiry, notable since she is part of House Speaker Nancy Pelosi’s leadership team and the speaker has counseled restraint.

“This is a personal decision on my part,” Schakowsky said in a video.

She added, “I think that our leadership has done a good job.

“But instituting the impeachment inquiry will actually enable us to get more information, more documents,” the Evanston Democrat said.

Opening an impeachment inquiry — even one that does not necessarily lead to the House voting on articles of impeachment — is slowly gaining support among House Democrats, though so far only some 60 of the 235 are on board, with Casten and Schakowky among the latest.

“An impeachment assumes that we will start the process, and you already know the outcome, and you know how you will vote in the final analysis once all the facts are in,” Casten said.

In contrast, he said, “an impeachment inquiry is saying we need to initiate the process of using every tool we have to get all those facts, of making them transparent, to doing it in a way that the public understands what we’re doing, understands the scope of what we’re doing, understands what we are, what we are learning and that we go into that with a completely open mind to know that at the end we will decide based on the facts.

“But we need to use every tool in our power to get those facts and to get those facts to the American public.”

Where an impeachment inquiry could lead – and whether he will pay a political price in 2020 for his stand, gets the same answer from Casten.

“I don’t know,” Casten said.

Casten, a Downers Grove resident, arrived on Capitol Hill in January, after beating former Rep. Peter Roskam, R-Ill., 53.6% to 46.4%. The 6th Congressional District hugs the Chicago suburbs and includes parts of Cook, DuPage, Kane, McHenry and Lake counties.

Once in Congress, Casten said he wanted to focus on climate change, his signature issue, plus health care, gun violence and campaign finance reform. Russian interference into the 2016 election — and Trump blocking investigative efforts — jumped on his plate in part because of his membership on the House Financial Services Committee subcommittee on Oversight and Investigations.

Casten said making his position public at this time is right for him, “in order to have a conversation with the public about what I know and why I’m concerned. I have to be honest about where I stood on this issue.

“When the president is actively frustrating our ability to find the information, we have to use every tool in our power to maximize transparency.”

Casten said he “struggled” over backing an impeachment inquiry and only locked in his decision after he read special counsel Robert Mueller’s report about abuse of power, pointing to the discussion on page 178 about “corruptly motivated conduct” and criminality.

“I’m not telling leadership what to do. I’m not telling other members what to do,” Casten said.

Casten arranged a meeting with House Speaker Nancy Pelosi last week to give her a heads up. Pelosi is not in favor of kicking off even an impeachment inquiry at this time.

A House impeachment of Trump does not remove him from office; it only sends the question to the Senate for a trial. Since the Republicans control the Senate — and it takes two-thirds of the Senate members present to convict — Trump would almost certainly remain in the White House.

On Wednesday, speaking to reporters at a breakfast hosted by the Christian Science Monitor, Pelosi said, “I don’t think you should have an inquiry unless you’re ready to impeach. … What I believe is that when we go forward, as we go forward, it has to go deep. It can’t be the Democrats impeach in the House; the Senate, in his view, exonerates, the Republicans exonerate in the Senate. This president must be held accountable.”

Rep. Bobby Rush, through a spokesman, is the only one from Illinois calling for impeachment. Reps. Mike Quigley, Jesus “Chuy” Garcia, Danny Davis and Schakowsky support launching an impeachment inquiry. Except for Casten, the other five represent safe Democratic districts.

Said Casten, “This is what I think has to be done, for me. And I think it’s important for the voters to know that.”