WASHINGTON — The nomination of Judy Shelton, one of President Trump’s picks for the Federal Reserve, received a lift on Wednesday after a key Republican senator who had expressed skepticism about her qualifications said he would support her candidacy.

Senator Patrick J. Toomey, Republican of Pennsylvania, said in a statement that he would back Ms. Shelton. That leaves two Republicans on the Senate Banking Committee who have expressed doubts about Ms. Shelton — Senator Richard C. Shelby, Republican of Alabama, and Senator John Kennedy, Republican of Louisiana.

Mr. Shelby remains undecided, his office said. Mr. Kennedy is also undecided, according to a person with knowledge of his thinking.

Ms. Shelton’s path to the Fed board remains difficult. She would need a simple majority vote by the Banking Committee to move onto confirmation by the full Senate, meaning opposition by only one Republican on the panel could potentially dash her chances of moving forward. The committee has 13 Republicans and 12 Democrats, and it is unclear that any of the Democrats would support her bid.