WASHINGTON – At every investigative avenue pursued by congressional Democrats is the Trump administration ready for a fight.

A request for the president’s tax returns? A letter from his attorneys demanding they remain secret. Testimony from key current or former aides? The White House is threatening to invoke executive privilege. Financial documents related to the president’s assets? Two separate lawsuits.

But on Wednesday, the fight is set to reach a new level as the House Judiciary Committee votes on whether to hold Attorney General William Barr in contempt of Congress after he refused to comply with a subpoena for special counsel Robert Mueller’s entire unredacted report.

The clash between the executive and legislative branches sets in motion a potential constitutional showdown over how much information the Justice Department must provide to Congress. The contempt vote, which followed an effort Tuesday between committee staff members and Justice Department officials, will take place Wednesday at 10 a.m. EDT. After the committee vote, the next step is for the full House to consider the resolution.

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House Judiciary Committee Chairman Jerrold Nadler, D-N.Y., said Barr’s failure to comply with the subpoena left no choice but to initiate contempt proceedings.

“Even in redacted form, the special counsel’s report offers disturbing evidence and analysis that President Trump engaged in obstruction of justice at the highest levels," Nadler said Monday in scheduling the vote. "Congress must see the full report and underlying evidence to determine how to best move forward with oversight, legislation, and other constitutional responsibilities."

But what is contempt of Congress, how does it work and could it actually lead to charges against Barr or other Trump officials who defy requests from Capitol Hill?

The most common method used by Congress has been criminal contempt; a charge is a misdemeanor and punishable by jail time of between a month and a year and a fine.

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But it's not as easy as simply charging someone. The measure doesn't have to pass in both the House and Senate and can start in committee, meaning in this case, Nadler could bring the issue before the House Judiciary Committee.

After it passes with a simple majority, it would move to a full vote in the House.

Once approved, the House speaker or the Senate president pro tem then turns the matter over to the U.S. attorney for the District of Columbia, "whose duty it shall be to bring the matter before the grand jury for its action," according to the law.

Hurdles and executive privilege

While Congress has broad investigative powers, there are limits. The Supreme Court has said that congressional inquiries should have a legitimate legislative purpose and should not be used for political purposes to embarrass, expose wrongdoing or target a particular person or group.

And holding someone in contempt of Congress has caveats and drawbacks. Jailing someone until they testify or offer up documents might seem like an easy solution but the CRS notes that Congress is not allowed to hold someone past the "end of the current session of Congress." The process could also likely end up worsening tensions between each branch of government and give the public a front-row seat to the chaos. Plus some, like Barr, have armed security and it's unclear what would happen if Congress attempted to arrest him.

And while a civil claim could be the path of least resistance, it could be time-consuming and delay an investigation. Even criminal contempt has a catch: It's up to the Justice Department to actually take up a criminal case against someone. In the past, the Justice Department has declined to prosecute criminal contempt-of-Congress cases.

There's also the question of executive privilege, which President Trump said was being considered to block his current and former aides from testifying before lawmakers.

It isn't clear whether Congress' contempt powers could trump the president invoking executive privilege as neither the White House nor Congress has sought a resolution to the question from the Supreme Court, both sides fearing they might lose.

Congress would have a harder time investigating presidents for decades to come if the high court ruled against it and if the White House lost, it would open the door for a multitude of congressional inquiries.

It's been used before, including on Obama officials

Congress rarely holds people in contempt. But it has done so in the past to force witnesses to appear or produce documents.

The last time Congress used its inherent contempt powers was in 1934 when the Senate held William MacCracken, a former member of Herbert Hoover's administration, after he refused a subpoena. The Senate had nowhere to hold MacCracken so he was imprisoned at a hotel, according to the Washington Post.

But Congress has voted on contempt charges more recently, even discussing using it against members of the Trump administration last year after former White House adviser Steve Bannon refused to answer questions.

Other examples include in 2012 when the House voted to hold then-Attorney General Eric Holder in contempt for declining to provide documents and in 2014 after IRS official Lois Lerner invoked her Fifth Amendment right against self-incrimination during a congressional hearing. In both cases, the Justice Department declined to bring criminal cases.

While a contempt charge normally moves through the criminal justice system and the courts, there's one final method that has gotten attention in recent days, given the president's reluctance to cooperate with congressional investigations.

Lawmakers can elect to pursue a contempt-of-Congress charge in an impeachment proceeding, which is a political process to remove the president from office that moves through Congress instead of the courts.

A contempt-of-Congress charge was one of the three articles of impeachment filed against President Richard Nixon in 1974 after he defied subpoenas for documents and information that Congress said it needed for an impeachment inquiry.

Contributing: Associated Press; Bart Jansen