WASHINGTON — House Judiciary Committee chairman Rep. Jerry Nadler, D-N.Y., is threatening to subpoena Attorney General William Barr, who has told the committee he may refuse to appear at a hearing Thursday unless members abandon their plan to have him questioned by staff lawyers.

It's one of many potential subpoena battles brewing between Congress and the Trump administration, which is showing an increasing willingness to stiff-arm congressional oversight committees.

So what practical options does Congress have to enforce its wishes?

No easy ones, as it turns out.

Congress has three methods at its disposal to seek compliance with a subpoena by holding a witness in contempt, according the Congressional Research Service. Each has problems.

Under the doctrine of "inherent contempt," the House or Senate could send members of its security force to arrest and detain the witness. There is precedent for this in U.S. history, but not recent precedent — it hasn't been used since 1935.

In the modern world, the House sergeant-at-arms isn't going to be able to arrest the attorney general, who is protected by an armed FBI security detail. As one former White House official once put it, only half in jest, "They have a lot of guns over there."

The second method involves seeking to hold a witness in criminal contempt under federal criminal statutes 2 U.S.C. §§192 and 194. The statutes make it a crime to fail to comply with a lawful congressional subpoena, and call for the House or Senate to refer a criminal contempt citation to the office of the U.S. Attorney for the District of Columbia, which can seek an indictment from a grand jury.

The problem with this in the current case: All federal prosecutors, including all 90-plus U.S. attorneys, work for Barr, and would be under no obligation to pursue a contempt charge.

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That leaves a third option — Congress can seek a civil contempt citation from a judge. The Judiciary Committee, for example, could sue Barr in district court, providing a simple majority of the full House voted to authorize such an action.

"If the individual still refuses to comply, he may be tried by the court in summary proceedings for contempt of court, with sanctions being imposed to coerce their compliance," the Congressional Research Service said in a 2017 paper.

A recent precedent for this happens to involve the House Judiciary Committee, then controlled by Democrats under the George W. Bush administration.

At issue was a congressional investigation into the firing of several U.S. attorneys.

The committee subpoenaed former White House counsel Harriet Miers, and the White House instructed her not to comply, citing executive privilege. It made the same instruction regarding a document subpoena to Josh Bolten, the White House chief of staff.

Both were held in contempt of Congress, and the speaker of the House asked the U.S. attorney in Washington, D.C., to pursue the matter.

But the federal prosecutor declined to do that, citing a Justice Department policy of not prosecuting a White House official for criminal contempt of Congress if that official had invoked executive privilege at the behest of the president.

Congress sued, and a district court judge sided with lawmakers. The Bush administration appealed and President Barack Obama took office while the case was still pending. The new administration settled the case, granting Congress access to some of the documents it sought and allowing sworn testimony from Miers.

By then, a year and a half after Congress issued the subpoena, the oversight issue largely was moot.

Much the same thing happened when the Republican-controlled House Oversight Committee sought to subpoena Attorney General Eric Holder in 2012 over a scandal involving a gun investigation known as Operation Fast and Furious.

This time, the Obama Justice Department refused to prosecute a congressional contempt citation against the attorney general. A court battle dragged on, and it wasn't until January 2016 that a court ordered the Justice Department to produce some documents. The Obama administration appealed, and the case lingered until President Donald Trump took office.

In March of last year, the Trump Justice Department settled the case by agreeing to release some records.

"The Department of Justice under my watch is committed to transparency and the rule of law," then-Attorney General Jeff Sessions said in a statement.

Now that it's Democrats making the demands, the ardor for transparency at the Justice Department appears to have cooled a bit.