Republican Congressman Doug Collins announced Wednesday a bid for the U.S. Senate in Georgia, teeing up a showdown with fellow GOP Senator Kelly Loeffler in the state's November special election.

Collins, a staunch ally of President Trump, confirmed the Senate run in an interview with "Fox and Friends" and on Twitter, where he said he had for months "given serious deliberation to the role I should serve that would best benefit GA, the country and @realDonaldTrump."

For months, I have given serious deliberation to the role I should serve that would best benefit GA, the country and @realDonaldTrump. Today, I have officially launched my campaign for Senate to do just that. I invite you to join our campaign here:https://t.co/xubaYUr5RP — Doug Collins (@CollinsforGA) January 29, 2020

The top Republican on the House Judiciary Committee and a four-term congressman, Collins has emerged as one of the most vocal opponents of the ongoing impeachment efforts against Mr. Trump and was named by the White House as a member of a GOP congressional delegation designed to advocate for the president and punch back against the Democrats' charges against him.

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Both of Georgia's seats in the U.S. Senate will be on the ballot come November, and Democrats are eyeing the state for a possible upset as they seek to take control of the upper chamber.

Under current law, Loeffler will face a jungle primary in November, meaning she and every other candidate, both Republican and Democrat, seeking the seat would face off on the same ballot. If no one receives 50% of the vote, a runoff would be held in January.

But the Georgia state legislature is working on a bill to eliminate the jungle primary, so instead, Loeffler would have to face a Republican primary against Collins in May.

Legislation that passed a subcommittee on Monday would scrap the jungle primary and hold a primary in May for this seat on the same day that the primary for Republican Senator David Perdue's seat — Perdue is also running for reelection — is held. The bill now moves to the full committee before being voted on by the state House.

Collins' announcement already sparked backlash from two Republican groups aimed at ensuring the GOP holds its majority in the Senate.

The National Republican Senatorial Committee said it is backing Loeffler in the contest and urged others to follow suit.

"The shortsightedness in this decision is stunning. Doug Collins' selfishness will hurt David Perdue, Kelly Loeffler, and President Trump. Not to mention the people of Georgia who stand to bear the burden of it for years to come," NRSC Executive Director Kevin McLaughlin said in a statement. "All he has done is put two Senate seats, multiple House seats, and Georgia's 16 electoral votes in play."

The Senate Leadership Fund, a super PAC aligned with Senate Majority Leader Mitch McConnell, also denounced Collins' Senate bid.

"It's so selfish of Doug Collins to be promoting himself when President Trump needs a unified team and Senator Loeffler is such a warrior for the president," Steven Law, the group's president, said in a statement. "As we've said before, Senator Loeffler is an outsider like Trump, not just another DC politician. We'll have her back if she needs us."

Georgia Governor Brian Kemp, a Republican, selected Loeffler in December to succeed Isakson, rebuffing political pressure to tap Collins for the seat. Isakson stepped down from the Senate due to health issues.

A financial services executive and part owner of Atlanta's WNBA team, Loeffler played up her conservative credentials and opposition to impeachment following the formal announcement and, now in Washington, has continued to defend Mr. Trump during the impeachment trial.

On Monday, Loeffler took aim at fellow Republican Senator Mitt Romney of Utah over his support for additional testimony during the proceedings.

"After 2 weeks, it's clear that Democrats have no case for impeachment. Sadly, my colleague @SenatorMittRomney wants to appease the left by calling witnesses who will slander the @realDonaldTrump during their 15 minutes of fame," she tweeted.

After 2 weeks, it’s clear that Democrats have no case for impeachment. Sadly, my colleague @SenatorRomney wants to appease the left by calling witnesses who will slander the @realDonaldTrump during their 15 minutes of fame. The circus is over. It’s time to move on! #gapol — Senator Kelly Loeffler (@SenatorLoeffler) January 27, 2020

In the past, however, Loeffler has been been a generous Romney backer, donating $750,000 to Restore Our Future, the super PAC affiliated with Romney's presidential run in 2012, according to FEC reports.