After early signs that some of President Trump’s unconventional cabinet choices could be derailed by Republicans alarmed at their character, disturbing paper trails and lack of expertise, the resistance has collapsed.

One after the other on Tuesday, Republican senators fell into line behind two of the president’s most baggage-laden nominees, Robert F. Kennedy Jr. for health secretary and Tulsi Gabbard for director of national intelligence.

The party-line committee votes to send both nominees to the floor for likely confirmation next week provided the clearest evidence yet that Mr. Trump’s pressure tactics and the threat of a barrage of abuse by his allies against would-be defectors had sapped whatever remained of a G.O.P. impulse to balk. And they suggested a broader impulse among Republicans on Capitol Hill — even the few who have maintained some degree of independence from Mr. Trump — to shrink from confrontation with him and allow him to have his way at the dawn of his second term.

The decision by Senator Todd Young of Indiana to back Ms. Gabbard, in conjunction with the announcement of Senator Bill Cassidy of Louisiana that he was setting aside personal reservations to back Mr. Kennedy, marked the end of any serious effort to stop Mr. Trump’s most divisive nominees.

Together with the narrowest possible confirmation of Pete Hegseth last month as secretary of defense, the moves constituted a surrender by Senate Republicans to Mr. Trump even in the face of serious qualms among some in the G.O.P. Another nominee who had initially been seen as facing a potentially difficult path to confirmation, Kash Patel for director of the F.B.I., has impressed Republicans and seems headed for approval as well despite strong Democratic objections.

Though a handful of senators had walked up to the edge of rejecting one or another nominee, putting their confirmations in peril, all but a very few backtracked in the end, issuing statements that they had received promises and assurances from both the nominee and the White House that had eliminated their chief concerns.