The GOP majority in the Senate is shaping up as a firewall for Republicans who are worried that President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE might falter and lose the White House next year.

Republicans see winning back the House majority as a tough climb in 2020, and head-to-head matchups between Trump and various Democratic presidential contenders show the president behind his potential challengers.

ADVERTISEMENT

Though Republicans overall are optimistic about Trump's reelection prospects, they see holding the Senate, where they have a 53-47 edge, as crucial given the shape of races for the White House and lower chamber. And they’re playing their cards accordingly.

“If we lose the presidency — and if I had to guess right now, the odds are 10 percent we get the House back — the Senate is the only check and balance,” said one former Republican Senate chief of staff. “If we don’t keep the Senate, we’re basically screwed. I hate to just cut to the chase, but that is exactly what the [National Republican Senatorial Committee] is running with.”

Senate Republicans have relished their power to sideline major Democratic bills passed by the House, including sweeping election reform and gun legislation.

They argue that maintaining a GOP majority in the Senate is a crucial failsafe against “socialist” policies — the Green New Deal and “Medicare for All” — that could be pursued by a Democrat in the Oval Office coupled with a Democratic-controlled House.

ADVERTISEMENT

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellDemocratic senator to party: 'A little message discipline wouldn't kill us' House to vote on resolution affirming peaceful transition of power Republican lawyers brush off Trump's election comments MORE (R-Ky.), the self-declared “Grim Reaper” for progressive legislation, has urged GOP incumbents to position themselves as a “firewall” against ideas being pitched by the field of Democratic presidential candidates.

"If I'm still the majority leader in the Senate think of me as the Grim Reaper ... I guarantee you that if I'm the last man standing and I'm still the majority leader, it ain't happening. I can promise you," McConnell said during a stop in Kentucky earlier this year.

The “firewall” narrative has trickled down to battleground Senate races, with GOP incumbents seizing on McConnell’s message.

"The socialism charge in particular works well with some of the soft Republican voters, suburban voters that Republicans have struggled with in the Trump era ... so I think you'll see a lot of Republican candidates talk about the Senate being the last firewall,” said a national GOP strategist watching the Senate races.

Sen. John Cornyn John CornynHillicon Valley: Productivity, fatigue, cybersecurity emerge as top concerns amid pandemic | Facebook critics launch alternative oversight board | Google to temporarily bar election ads after polls close Lawmakers introduce legislation to boost cybersecurity of local governments, small businesses On The Trail: Making sense of this week's polling tsunami MORE (R-Texas), who is up for reelection next year, referred to the Senate as a “graveyard” for “disastrous socialist policies.” And at a campaign event for Sen. Cory Gardner Cory Scott GardnerBreaking the Chinese space addiction Trump dumbfounds GOP with latest unforced error Billionaire who donated to Trump in 2016 donates to Biden MORE (R-Colo.) last week, former United Nations Ambassador Nikki Haley Nimrata (Nikki) Haley'The soul' versus 'law and order' Author Ryan Girdusky: RNC worked best when highlighting 'regular people' as opposed to 'standard Republicans' GOP lobbyists pleasantly surprised by Republican convention MORE said the country would “see socialism take over” if the Gardner loses his reelection bid in 2020.

Republicans are defending 22 seats compared to the 12 in play for Democrats. Most GOP incumbents are running in deeply red states, limiting the Senate battlefield to a handful of states: Arizona, Colorado, Maine and North Carolina, where GOP Sens. Martha McSally Martha Elizabeth McSallyOn The Trail: Making sense of this week's polling tsunami The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE, Gardner, Susan Collins Susan Margaret CollinsDemocratic senator to party: 'A little message discipline wouldn't kill us' Poll: 57 percent of Americans think next president, Senate should fill Ginsburg vacancy On The Trail: Making sense of this week's polling tsunami MORE and Thom Tillis Thomas (Thom) Roland TillisOvernight Energy: Trump officials finalize plan to open up protected areas of Tongass to logging | Feds say offshore testing for oil can proceed despite drilling moratorium | Dems question EPA's postponement of inequality training On The Trail: Making sense of this week's polling tsunami Feds say offshore testing for oil can proceed despite drilling moratorium MORE, respectively, are on the ballot.

Democrats need to pick up either three or four seats in 2020, depending on which party wins the White House, to gain control of the chamber. They also need to hold on to Democratic Sen. Doug Jones’s seat in Alabama, where Republicans are feeling bullish about their chances of unseating the first-term senator.

The push to highlight the importance of keeping the Senate in GOP hands comes as handicappers and strategists are predicting that Republicans are unlikely to pick up the 18 seats needed to retake the House in 2020.

And Republicans consider the White House in play after Trump carved an unusual path to the presidency — including winning traditionally Democratic states like Michigan, Pennsylvania and Wisconsin — that could be tough to replicate in 2020. A Fox News poll this month found Trump trailing four leading Democratic presidential hopefuls in head-to-head matchups.

"The House is going to be a pretty tough road to win back this cycle. The presidential race, it's kind of like who really knows at this point. But the Senate is a safer bet,” the national GOP strategist said, adding it could "easily be a possibility" that Democrats win the White House and Republicans hold onto the Senate.

Republicans say they are cautiously optimistic about their chances for keeping the Senate, but they aren’t taking any chances.

GOP Senate candidates have raised more than $80 million so far this election cycle, compared to more than $61 million for Democratic candidates, according to the Center for Responsive Politics. Additionally, the National Republican Senatorial Committee has outspent and outraised its Democratic counterpart, the Democratic Senatorial Campaign Committee (DSCC), this cycle. A DSCC spokesperson noted Tuesday that the Democratic campaign arm outraised its GOP counterpart in July and has more cash on hand — roughly $16.9 million, compared to $11.7 million for Republicans.

“Donors are no different than when some of us go to Vegas for a long weekend,” one Republican consultant said. “They want to bet on the winner. No one is going to invest in something they don’t think is going to win.”

While there’s a growing sense among Republicans that the Senate may be their best hope of holding on to a lever of power in Washington, some Republican incumbents are already seen as being on the chopping block. One GOP operative who has worked on Senate races predicted that Gardner, perhaps the most at-risk GOP incumbent, would lose his seat, saying his fate was all but decided.

“Cory is a great guy and a great candidate, but he’s f---ed,” one GOP operative who has worked on Senate races said. “RIP Cory Gardner.”

In turn, the operative said, Republicans would be forced to pour hundreds of millions of dollars into defending other vulnerable senators, notably McSally and Collins, who have already drawn high-profile Democratic challengers.

“If it’s a tight presidential, it’s really going to boil down to this: What amount of money would you not spend [to hold the Senate]?” the operative said.

--This report was updated at 10:23 a.m.