"He can't effectively serve the president," Brown said Wednesday on a local Boston-area radio program, "Nightside With Dan Rea," as first reported by the Boston Herald.

“For the best interest of the country, I think he should step down and resign. He’s lost the confidence of the American people. Certainly he’s lost the confidence of Congress. He misled Congress. They have a right to know,” said the freshman GOP senator.

Brown is the latest in a growing number of GOP lawmakers calling on the attorney general to step down in the wake of congressional investigations into the ATF’s botched Fast and Furious gun-tracking operation.

Last week, Florida Sen. Marco RubioMarco Antonio RubioGOP Senate candidates trade barbs in brutal Indiana primary Students gather outside White House after walkout to protest gun violence Overnight Energy: Senate confirms Bridenstine as NASA chief | Watchdog probes Pruitt’s use of security detail | Emails shine light on EPA science policy changes MORE said lawmakers had “reached the point of no return” and that Holder had no choice but to leave office.

The House Oversight Committee voted last week along party lines to recommend a contempt citation for the embattled attorney general, claiming he failed to respond to a subpoena for documents related to the Fast and Furious probe. The vote by the House is expected on Thursday.

Chairman Darrell Issa (R-Calif.) has accused the administration of obstructing the investigation after President Obama asserted executive privilege last week to withhold documents on the DOJ operation.

Democrats, though, accuse the House GOP of using the probe to score political points and embarrass Obama and Holder. 

Brown repeated calls for the administration to turn over documents requested by House GOP lawmakers. “There should be a full and fair exchange of information so we can get to the bottom of it,” he said.

The Republican senator is locked in a tight race with Democratic challenger Elizabeth WarrenElizabeth Ann WarrenDem senators demand Trump explain ties to Koch brothers 'Fearless Girl' statue to be moved away from Wall Street bull Sanders, Warren, O’Rourke inspire patriotic small donor waves MORE, who quickly blasted his stance, saying the attacks on Holder were “all about politics.” 

“The Republicans think they’ve got something here, and he’s just trying to see if he can turn up the temperature on it. I think this is why people get disgusted by politics,” she said during an appearance on MSNBC’s “Rachel Maddow Show.”