(CNN) Tennessee Sen. Lamar Alexander, a senior and influential Republican, implored President Donald Trump on Thursday to find other pots of money available to him to build a border wall with Mexico and avoid going forward with his declaration of a national emergency.

Alexander said doing so would mean there would not be a "dangerous precedent" of a president using the emergency declaration to go directly over the will of Congress, which in this case voted to deny him those border wall funds.

It would also avoid a possible constitutional clash between the legislative and executive branches, as Congress weighs a resolution of disapproval to kill the emergency declaration with a key vote in the Senate expected sometime in the next two weeks after it passed the House Tuesday

Alexander, who has not announced how he will vote on that resolution, raised his concerns the same day another Republican senator, Rand Paul of Kentucky, signaled he may vote against Trump on the issue.

"What I would like him to do is take another look at his existing authority and if he has sufficient funds to build 234 miles of wall, to use that," Alexander told reporters after delivering a floor speech on the issue. "From his point of view, it should avoid litigation, make sure the wall gets built, and avoid this dangerous precedent that I believe is unnecessary."

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