The Senate on Monday voted along party lines to advance the nomination of Tulsi Gabbard to be the director of national intelligence, signaling the collapse of Republican resistance to her nomination and placing her on a smooth path to confirmation.

The 52-to-46 vote was the latest sign that Republicans, facing intense pressure from President Trump to confirm his nominees, are willing to drop serious reservations and capitulate to his wishes. It cleared away the final hurdle to Ms. Gabbard’s confirmation, once thought to be an uphill battle in the Senate amid strong bipartisan concerns about her positions on intelligence matters and sympathetic statements about the former Syrian dictator Bashar al-Assad and President Vladimir V. Putin of Russia.

She is now all but certain to be confirmed in a final vote to be held either late Tuesday evening or early Wednesday.

The action came as Democrats, who have called Ms. Gabbard unfit for the role, pressed their Republican colleagues to join them in opposition.

Senator Mark Warner of Virginia, the top Democrat on the intelligence committee, said it would be “irresponsible” to confirm Ms. Gabbard, calling her unfit to lead the 18 agencies that make up the intelligence community in the United States.

“The world today is more complex and more dangerous than ever before; we need serious people with the experience, expertise and judgment to navigate that complexity,” Mr. Warner said in a speech moments before the vote. “Unfortunately, Ms. Gabbard is not such a nominee.”