Senate Republicans are locking arms to defend the filibuster — putting them on a potential collision course with former President Trump if he wins back the White House.

Why it matters: Senate Republican Leader Mitch McConnell (R-Ky.) repeatedly rebuffed demands by Trump to kill the filibuster during his presidency. Republicans — even top Trump allies — are uniting to hold the line in McConnell's future absence.

• Dismantling the filibuster — a Senate rule that effectively requires 60 votes to pass legislation — would make it easier for Trump to jam through key legislative priorities on the border, taxes, elections or abortion.
• That higher threshold makes it much harder to move legislation without bipartisanship.
• But privately, some GOP offices Axios contacted were concerned about being viewed as out of step with Trump on the issue.

Zoom in: Nearly every member of current GOP leadership — and those vying for future spots — is a public defender of the filibuster.

• For GOP leader: Sens. John Cornyn (R-Tex.) and John Thune (R-S.D.) say the filibuster is part of the Senate as an institution and must be protected.
• For No. 2 GOP leader: Sen. John Barrasso (R-Wyo.) — a Trump ally who is likely to win the No. 2 job — says "the filibuster is the character of the United States Senate. I continue to support the filibuster."
• For No. 3 GOP leader: Sens. Joni Ernst (R-Iowa) and Tom Cotton (R-Ark.) railed against Democrats for threatening to eliminate the filibuster in 2022 to pass voting rights legislation. Both are running for the No. 3 position, but Cotton is expected to have the edge.

Between the lines: Some Republicans have come to recognize how Democrats could use the end of the filibuster to accomplish liberal wish list items, like making D.C. a state, a senior GOP aide told Axios.

• "I'll tell you why my thinking evolved on that," Sen. Steve Daines (R-Mont.) told Axios. "It's because we see what the Democrats would do."
• Trump has encouraged Daines, who leads the National Republican Senatorial Committee — to run for GOP leader.
• Daines said he was confident a majority of the Republican caucus were on the same page with keeping the filibuster.

What to watch: Republican candidates running in key states that could give Republicans the majority are also unwilling to eliminate the 60-vote threshold.

• Even close Trump ally Kari Lake, who is running for Senate in Arizona, wants to protect the filibuster.
• It puts her in line with Trump-antagonist Larry Hogan in Maryland, who has vowed to "stand up to Republicans and Democrats who try eliminate the filibuster," according to Hogan's team.
• Dave McCormick, running in Pennsylvania, said the "filibuster protects America from being subject to the whims of the majority" — and a spokesperson for Tim Sheehy in Montana said he "believes in preserving the filibuster."