Senate Democrats have dug in their heels to stall confirmation proceedings for President Donald Trump’s Cabinet nominees.

Though the Senate confirmed two of Trump’s nominees Friday and a third Monday evening, Democrats have slowed the pace considerably compared with Republicans’  treatment of President Barack Obama’s choices.

Democrats can’t put off  final votes indefinitely because Republicans hold 52 seats in the Senate and a simple majority of 51 votes is needed to confirm most presidential nominations. Democrats, however, are able to use several procedural tactics to slow down the confirmation process.

Senate rules and procedures allow Democrats to employ three basic tactics to delay confirmation votes on a president’s appointments, Rachel Bovard, director of policy services at The Heritage Foundation, told The Daily Signal:

1. Strictly Adhering to Committee Meeting Times

Most presidential appointments requiring Senate confirmation are taken up by one or more committees, which review the nominee, hold hearings, and vote to report the nominee favorably or unfavorably to the full Senate.

Senate rules permit committees to meet and conduct business at certain times of the day, although senators routinely waive these rules.

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Democrats may choose to adhere to the rules as a way to slow down the process, Bovard, a former Senate aide, said.

“Those rules are routinely waived to allow committee business to be conducted during the full workday, but Democrats could object to this, and in doing so, dramatically slow down the process of confirmations,” she said.

“It’s the right of the Dems to object to its waiver. So the GOP would just have to slow down and comply with it.”

Trump picks targeted for delay by Senate Democrats include Exxon Mobil Corp. CEO Rex Tillerson for secretary of state; Sen. Jeff Sessions, R-Ala., for attorney general; philanthropist Betsy DeVos for secretary of education; Rep. Mike Pompeo, R-Kan., for CIA director; businessman-investor Wilbur Ross for commerce secretary; retired neurosurgeon Ben Carson for secretary of housing and urban development; and Rep. Tom Price, R-Ga., for secretary of health and human services. Only the CIA directorship is not an official Cabinet post.

The Senate voted Monday night to confirm Pompeo, 66-32, with only one Republican—Rand Paul of Kentucky—voting no. Earlier, the Foreign Relations Committee narrowly approved Tillerson along party lines, 11-10, and sent his nomination to the full chamber.

Friday, the Senate confirmed two retired Marine generals: James Mattis as defense  secretary and John Kelly as homeland security secretary.

2. Preventing a Quorum for Committee Meetings

Senate committees can’t conduct business without a minimum number of members present–called a quorum–and Democrats could fail to turn up to provide that quorum.

“It depends on the committee, but you have to have a minimum number of committee members there to conduct business,” Bovard said.

A total of 51 senators must be present to provide a quorum for official business on the Senate floor. Because Republicans have 52 seats, this is not much of an obstacle.

Although the minimum attendance number varies for each committee, preventing a quorum can be a viable delaying tactic for disapproving Democrats.

For the Senate Judiciary Committee, for example, “seven members of the committee, actually present, shall constitute a quorum for the purpose of discussing business,” according to its rules.

To move forward, the rules say, “nine members of the committee, including at least two members of the minority, shall constitute a quorum for the purpose of transacting business.”

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The Judiciary Committee, which is considering Sessions’ nomination for attorney general, is comprised of 11 Republicans and nine Democrats.

“The Judiciary Committee hasn’t had an issue reaching a quorum yet,” Bovard said. “My understanding is that they just haven’t scheduled the vote because they’re reviewing paperwork.”

The quorum route actually could give Republicans an easier ride, she said:

Committees all have different rules, but some of them don’t require both Democrats and Republicans to be present. So, if all the Republicans show up and none of the Democrats [do], there would still be a quorum in some committees. The Republicans would just need to make sure all their people are there.

3. Using Paperwork Tactics

Senate Democrats also may choose to request additional paperwork on nominees, or request additional time to review paperwork.

“They’ll pitch a fit about demanding paperwork,” Bovard said. “They can’t actually delay anything with that, but they could make a PR case for delay … basically just like, ‘Why are we considering this?’”

This tactic has been somewhat successful, for example, in delaying committee action for DeVos,Trump’s nominee for secretary of education.

The Office of Government Ethics took a significant amount of time in reviewing DeVos’ paperwork, NBC News reported.

The Trump transition team said Jan. 17 that a certified ethics agreement and financial disclosure statement, which would disclose conflicts of interest she might have if confirmed, was submitted in December, the network reported.

However, the ethics office did not release its report on DeVos to the Health, Education, Labor and Pensions Committee until Friday, The Washington Post reported.

The committee rescheduled a vote from Jan. 24 to Jan. 31.

The Judiciary Committee was on a course to delay a vote on Sessions, Trump’s nominee to head the Justice Department as attorney general.

Sen. Dianne Feinstein, D-Calif., the committee’s ranking member, said Monday she intends to request a delay from Tuesday’s scheduled vote “to give the committee more time to conduct its due diligence,” ABC News reported.

Judiciary Committee rules allow any member to hold a vote over until the next week, meaning a Jan. 31 vote on Sessions.

Opposition from one or more senators also may prevent a floor vote on a nomination that has come out of committee, because the rules require “unanimous consent” to consider and confirm a nomination.

If a nominee faces substantial opposition, Senate Majority Leader Mitch McConnell, R-Ky., may wish to end debate through a procedure called cloture. Under it, a simple majority of senators voting—normally 51—is able to limit debate to 30 hours and advance the nominee to a floor vote.

Senate Minority Leader Chuck Schumer, D-N.Y., angered Republican leaders by breaking a promise that Pompeo, Trump’s pick for CIA director, would be confirmed by voice vote on Inauguration Day, The Weekly Standard reported.

Schumer backed out of his promise, according to the report, telling Sen. Tom Cotton, R-Ark.: “I said that I would not block him. I never said that I could speak for 47 other Democrats.”

Monday night, Schumer voted to confirm Pompeo.

Senate Democrats may be able to significantly stall the confirmation process, Bovard told The Daily Signal, but she is confident Sessions, DeVos and Trump’s other nominees will be confirmed.

“They can’t do that much, to be honest,” Bovard said.

Ken McIntyre contributed to this report, which has been updated to include the Senate vote confirming Mike Pompeo as CIA director.

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