WASHINGTON (Reuters) - The top Democrat in the U.S. Senate, Chuck Schumer, decried what he called undue haste to confirm President-elect Donald Trump’s nominations for various top posts, saying on Monday they needed more thorough vetting.

Hearings start on Tuesday for the Republican president-elect’s choices for senior administration posts, beginning with U.S. Senator Jeff Sessions, nominated to be attorney general, and retired General John Kelly, Trump’s pick for secretary of homeland security.

Schumer said Trump’s nominees, many of whom have extensive business backgrounds at companies such as Exxon Mobil Corp and Goldman Sachs, should be carefully scrutinized to be sure they avoid conflicts of interest.

“We’re not doing this for sport. Democrats feel very strongly that pushing for a thorough and thoughtful vetting process is the right thing to do,” Schumer said in a speech.

Republicans, who control the majority in the Senate, are presenting the Democratic objections as political grandstanding, saying they moved quickly eight years ago to confirm Democratic President Barack Obama’s Cabinet picks, approving seven the day he began his first term.

Schumer said some of Trump’s nominees have not completed a review process conducted by the U.S. Office of Government Ethics.

Trump transition spokesman Sean Spicer said on Monday that every nominee with a hearing this week has turned in the required paperwork.

“Everybody will be properly vetted as they have been in the past,” said U.S. Senate Republican leader Mitch McConnell, speaking in New York after meeting with Trump on Monday. He said he hoped to confirm six or seven national security appointees by the time Trump takes office on Jan. 20.

Trump needs to keep the 52 Republicans in the 100-seat Senate on his side to secure the simple majority votes needed for confirmations.

One of the more contentious hearings could be over Rex Tillerson, nominated for secretary of state. Trump’s stated desire for warmer relations with Russia comes at a deeply sensitive moment, after U.S. intelligence agencies concluded that Moscow used cyber hacking and other methods to try to tilt the U.S. presidential election in Trump’s favor over Democrat Hillary Clinton.

Republicans including U.S. Senator John McCain and U.S. Senator Lindsey Graham, veterans in foreign policy and security issues, have signaled concerns about Tillerson’s ties to Russia during his tenure as the chief executive of Exxon Mobil. Transition officials expressed confidence that Tillerson would win the pair’s support.

Sessions is also likely to face a thorough grilling, with critics arguing he obstructed civil rights protections in the past.

Democrats are likely to question nominees for positions related to national security about Trump’s proposal to build a wall along the U.S. border with Mexico and his pledge to temporarily suspend immigration from regions deemed to be exporting terrorism.

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The Trump team has put the nominees through mock hearings that are standard practice ahead of such events. Questions have included the kind of everyday concerns that periodically upset nominees for high office, such as the price of a gallon of gas. Each mock-up has also included at least one disruptive pretend protester, a transition official said.

Transition officials say they believe they could pick up Democratic votes from senators facing 2018 re-election bids in states Trump won on Nov. 8, such as U.S. Senator Claire McCaskill of Missouri.

Trump voiced optimism about the process on Monday, telling reporters at his office and residence in New York, “The confirmation is going great. I think they’ll all pass.”