Tennessee GOP Sen. Lamar Alexander told President Trump on Thursday that he should reconsider his decision to declare a national emergency at the southern border or face a possible Republican rebellion.

Alexander, who is retiring, refused to say whether he would join three other Republicans — Susan Collins of Maine, Thom Tillis of North Carolina and Lisa Murkowski of Alaska — in voting against the declaration.

With the Senate split 53-47, including two Independents who caucus with the Dems, the resolution would go down to defeat if a fourth Republican joined them.

But Trump has promised to veto any bill that would overturn his declaration in response to what he calls a “crisis” at the Mexican border, and it seems unlikely that the House and Senate could amass the two-thirds majorities that would be needed to override a veto.

Alexander said on the Senate floor that Trump had other ways to collect $5.7 billion for the border wall.

“He’s got sufficient funding without a national emergency, he can build a wall and avoid a dangerous precedent,” Alexander told reporters afterward.

“That would change the voting situation if he were to agree to do that.”

Meanwhile, a small bipartisan group of senators planned to introduce a resolution Thursday aimed at blocking the declaration.

The proposal is identical to the one-sentence measure the Democrat-controlled House approved earlier this week.

“It shows support from senators for the resolution, not just House members,” Collins said.

The senators’ move was the latest evidence that significant numbers of lawmakers are not shying away from a fight with Trump.

The showdown puts some GOP lawmakers in an uncomfortable political crunch, with many leery of opposing Trump and angering his base of supporters.

But they also fear the precedent his move would set for future Democratic presidents to declare emergencies for their own purposes, and worry that the money he would shift to barrier construction could come from home-state projects.

The other sponsors are Sens. Tom Udall of New Mexico and Jeanne Shaheen of New Hampshire, both Democrats, and Murkowski, the only one not facing re-election next year.

Under a 1976 law, the resolution cannot be filibustered and would need only a simple majority of 51 votes to pass in the Senate.

The emergency would let Trump divert $3.6 billion now intended for military construction projects to erect more border barriers.

He’s invoking other authorities to transfer an additional $3.1 billion for construction.

In legislation that ended the 35-day partial federal government shutdown, Congress limited spending for barriers to just under $1.4 billion.

Several lawsuits have also been filed aimed at derailing the declaration, which could at least prevent Trump from getting the extra money for months or longer.

With AP