Some House Republicans are calling for the impeachment of Internal Revenue Service Commissioner John Koskinen, seen here in a file photo. (EPA/MICHAEL REYNOLDS)

Conservative lawmakers went to the House floor Tuesday to force a vote on the impeachment of Internal Revenue Service Commission John Koskinen, setting up a showdown that has pitted hard-right members against not only Democrats but also Republicans wary of a partisan battle weeks before the election.

The impeachment effort is rooted in the controversy over the IRS’s treatment of conservative nonprofit groups and the handling of subsequent congressional investigations.

Reps. John Fleming (R-La.) and Tim Huelskamp (R-Kan.), members of the conservative House Freedom Caucus, called up their impeachment measure Tuesday afternoon. Under House rules, as a “privileged” motion, the measure must come up for a vote no later than Thursday.

If the measure passes by a majority vote, it would set up a Senate trial of Koskinen — the first impeachment trial since U.S. District Judge Thomas Porteous was impeached in 2010.

Still, many Republicans are skeptical that Koskinen’s alleged misconduct rises to the level of impeachment, and they are wary of the precedent that might be set: Koskinen would be the first executive official below the rank of president to face impeachment proceedings since 1876.

Fleming, who is amid a Senate campaign, accused Koskinen on Tuesday of “high crimes and misdemeanors” for failing to comply with congressional subpoenas related to the IRS targeting investigation and presiding over the agency when records germane to that investigation — backups of emails from key official Lois Lerner — were improperly destroyed by an agency official. Koskinen, the IRS and congressional Democrats have strongly denied any wrongdoing.

Koskinen and his lawyers have argued directly to Republicans recently that, even if they believe he should be impeached, any impeachment should follow the standard impeachment process — which involves action by the House Judiciary Committee to send article of impeachment to the floor. The committee has not moved forward with those proceedings, to the frustration of House conservatives.

“Regular order and due process — including specific, evidence-based findings of fact — are particularly important here because the allegations against Commissioner Koskinen seem to change by the day,” attorneys for Koskinen wrote in a Thursday letter to Judiciary Committee leaders. They noted that the charges leveled by Fleming and Huelskamp “conflict with the findings of lengthy, probing investigations conducted by nonpartisan professionals.”

Koskinen’s defenders frequently cite a 2015 report from a Republican-appointed Treasury Department inspector general that concluded there was no evidence that the email backups were intentionally destroyed with the intent of keeping records from investigators.

IRS spokesman Matt Leas said Koskinen “remains focused ‎on the critical work needed for the nation’s tax system” and spent Tuesday addressing a meeting of tax professionals in San Diego. There, Leas said, Koskinen discussed “ongoing steps the IRS is taking to address challenges including taxpayer service, tax enforcement and cybersecurity.”

Koskinen met with two groups of House Republicans last week to personally present a case for why he should not be impeached. He appeared on Capitol Hill at the invitation of the Tuesday Group, an organization of GOP moderates who have largely been skeptical of the impeachment effort, and later met with approximately 40 members of the larger Republican Study Committee.

House Republicans are scheduled to discuss the impeachment issue together behind closed doors on Thursday, but Fleming told reporters Monday that he did not necessarily believe the meeting was necessary ahead of the vote. “I don’t see the point in that,” he said.

GOP leaders have handled the issue with kid gloves. Majority Leader Kevin McCarthy (R-Calif.) told reporters last week that the matter should be handled through “regular order” — in other words, by the relevant House committees — rather than through a special “privileged” resolution that comes straight to the floor.

“You have members on both sides of this,” House Speaker Paul D. Ryan (R-Wis.) said, “and this is something where the conference is going to work its will.”

Judiciary Committee Chairman Bob Goodlatte (R-Va.) held a hearing on the allegations against Koskinen in June, but he has stopped short of a formal impeachment proceeding. The House Oversight and Government Reform Committee, which does not have formal jurisdiction over the IRS or impeachments, passed a censure resolution in a party-line vote in June.

While those Republicans might be skeptical of the impeachment push — especially one pursued outside of the standard process — they might find it politically uncomfortable to oppose the measure on the House floor. And the Freedom Caucus members have done little to ease that discomfort.

“If you vote any other way other than voting for impeachment, you’re standing with the IRS and the Obama administration,” Huelskamp said Tuesday.

Lisa Rein and Kelsey Snell contributed to this report.