Republicans are amping up efforts to retain their Senate majority through a pair of Georgia runoffs that they view as a "firewall" against Democrats' agenda after President Trump lost his reelection bid. 

Sens. Kelly Loeffler and David Perdue are trying to beat back respective challenges from Democratic candidates Raphael Warnock and Jon Ossoff in Jan. 5 contests that will determine which party controls the Senate. If Ossoff and Warnock win, Democrats would secure a 50-50 split in the upper chamber, with Vice President-elect Kamala Harris then casting tie-breaking votes.

“We are the last line of defense,” Perdue said Tuesday during an interview on "Fox & Friends." “These two seats here will determine the majority in the Senate. Because of that, we're going to deny [Sen. Chuck] Schumer that majority, protect everything that President Trump has accomplished in the last four years, and make sure that the people of Georgia know that.”

SENATE REPUBLICANS TOUT MAJOR INVESTMENT IN GEORGIA RUNOFF ELECTIONS

Meanwhile, Senate Majority Leader Mitch McConnell and Sen. Todd Young, the departing chairman of the National Republican Senatorial Committee, are telling their GOP colleagues that each needs to help Perdue and Loeffler keep their seats, according to The Wall Street Journal, which cited GOP aides. 

Republicans are joining forces to help Perdue and Loeffler raise cash for what could become two of the most expensive races in history; the Georgia Battleground Fund -- the joint fundraising venture between Loeffler, Perdue and the NRSC -- is a 50-state operation. Both parties are expected to spend an exorbitant amount in the coming weeks. 

Sens. Joni Ernst, R-Iowa, and Marco Rubio, R-Fla., have both held rallies for their GOP colleagues in Georgia, while Sen. Rob Portman, R-Ohio, joined McConnell at a virtual event with supporters on behalf of Perdue and Loeffler, the Journal reported. McConnell has three more virtual events planned for next week. 

GEORGIA SENATE RUNOFF ELECTION AD SPENDING ALREADY TOPS $120 MILLION

The Journal also reported that Sen. Ted Cruz, R-Texas., is working with the conservative group Club for Growth to raise $10 million for the runoffs and to mobilize a group to knock on 1 million doors by Jan. 5.

“We have a battle on our hands right now, folks. It’s going to be a long one. We are the firewall. Not just for the Senate, but the future of our country,” Loeffler said during a campaign event two weeks ago. “We will be your voice in Washington if you’re our voice on Jan. 5.”

She reiterated that message again on Tuesday, saying Republicans "must save our country" after a conservative commentator tweeted that Democrats would end the filibuster, expand the Supreme Court, hike taxes and slash military spending if they won control of the Senate. (A moderate Democratic senator, Joe Manchin of West Virginia, has already effectively shot down Democrats' chances of nixing the filibuster and expanding the court).

CLICK HERE FOR THE LATEST FOX NEWS REPORTING ON THE GEORGIA RUNOFFS

Vice President Mike Pence will campaign for the two senators, and Trump indicated Thursday that he also plans to travel to the Peach State to help Loeffler and Perdue win their races.

“I spoke with the two great senators today,” Trump told reporters on Thanksgiving after a virtual call with U.S. troops stationed abroad on Thursday. "I’ll probably be going on Saturday."