As President Trump's pick to lead Veterans Affairs skids to a halt, senators from both parties are voicing frustration that the White House is skipping crucial vetting of nominees and leaving lawmakers to clean up the mess.

That sentiment was evident Tuesday on Capitol Hill after senators delayed hearings for White House physician Ronny Jackson, Mr. Trump's surprise pick to head the VA after he ousted former VA Secretary David Shulkin on Twitter. Jackson is facing questions about improper workplace behavior, and even Trump himself acknowledged that there were concerns about his nominee's experience.

"The White House still seems to be feeling its way on the nomination process," said Sen. Susan Collins, R-Maine, "and does not fully appreciate how important it is to do a thorough vetting and FBI background check on nominees."

Sen. John Thune, R-S.D., said that while lawmakers want to be "deferential as much as we can" to the president's preferences for his Cabinet, "it would be nice to know some of the issues that come up after the fact before the fact."

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Thune, asked by CBS News' Ed O'Keefe how much patience GOP senators have left for these kinds of nominees, said it's "pretty thin."

Mr. Trump, who promised to fill his administration with the "best people," often gravitates toward advisers he has a personal connection with or who look the part, drawing on the approach he took as a business executive. But as president, the result is a growing list of Cabinet secretaries and other officials who do not appear to undergo the rigorous scrutiny typically expected for White House hires.

Andy Puzder, Mr. Trump's initial choice to lead the Labor Department, stepped aside before his confirmation hearings, in part over taxes he belatedly paid on a former housekeeper not authorized to work in the United States. Health and Human Services Secretary Tom Price won confirmation, but ultimately resigned amid disclosures about his expensive travel habits.

Others are fighting similar charges, most notably Scott Pruitt, the embattled head of Environmental Protection Agency. Pruitt faces multiple allegations of improper housing, expensing and other practices, prompting several lawmakers to call for him to step down.

The Senate has increasingly become a partisan battleground for nomination fights, a war that escalated when President Barack Obama was in the White House and Senate Democrats, who had majority control, changed the rules to allow majority vote for confirming most nominees — the so-called nuclear option — to get around GOP filibusters.

Republicans returned the favor once Mr. Trump was in the White House, and they had the Senate majority, deploying the tactic to seat Neil Gorsuch on the Supreme Court.

Some GOP senators argue that Democrats are slow-walking even those Trump nominees with a solid track record, including Mike Pompeo, who got votes from 14 Democrats and one aligned independent last year during his confirmation for CIA director. Pompeo is now in line to run the State Department, but has faced stiff opposition from some of the same Democrats who backed him a year ago.

The Democratic opponents are going to "embarrass themselves," said Sen. John Cornyn, R-Texas. Thune called it "really a new low."

But questions about the White House's vetting standards have no doubt given Democrats fresh ammunition to challenge Mr. Trump's Cabinet picks.

"Our Republican colleagues bemoan the pace of the nominations," said Senate Minority Leader Chuck Schumer, D-N.Y. But he said because of the administration's "quick, sloppy vetting process," the Senate job of vetting nominees "is more important than ever before."

Sen. Patty Murray, D-Wash., said senators don't have to agree with a nominee's position on the issue, but the Senate has a historic role — to advise and consent — that the president's picks are up to the job.

"We're not going to allow nominees to be jammed through without proper scrutiny and debate," Murray said. "Now hopefully, the events of the last 24 hours have made it very clear why this is so important."

Asked about the adequacy of vetting process Tuesday, Senate Majority Leader Mitch McConnell said that such questions are better raised with the White House.

"Look," McConnell said, "it's up to the administration to do the vetting."

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Associated Press writers Alan Fram and Andrew Taylor in Washington contributed to this report.