(CNN) Republican Sen. Susan Collins said Tuesday she will vote against Chad Readler, President Donald Trump's nominee for the Sixth Circuit Court of Appeals who has come under fire from Democrats for being a lead lawyer for the Justice Department when it declined to defend key provisions of the Affordable Care Act in response to a lawsuit filed by Republican state attorneys general.
Collins, a rare GOP defender of Obamacare, cited in her statement announcing her decision Readler's role in the case as reason for opposing him.
"As the Acting Assistant Attorney General of the Justice Department's Civil Division, Mr. Readler was both a lead attorney and policy advisor in the Department's decision not to defend the Affordable Care Act, including its provisions protecting individuals with pre-existing conditions," she said. "Rather than defend the law and its protections for individuals with pre-existing conditions -- such as asthma, arthritis, cancer, diabetes, and heart disease -- Mr. Readler's brief in Texas v. United States argued that they should be invalidated."
Readler faces a key procedural vote at 4 p.m. ET on Tuesday when Republicans will try to break a Democratic filibuster of him. It's not clear if any other GOP senators will join her in opposing Readler. When Sen. John Thune of South Dakota, the Republican whip, was asked if Republicans would hold together to advance the nominee, he replied, "hopefully we'll have enough."
He later said he expects to get the simple majority needed.
All Democrats are expected to oppose Readler.
"One of the most dangerous decision to come out of the Trump administration in the last two years, was to not defend the Constitutionality of protecting pre-existing conditions in court," said Senate Minority Leader Chuck Schumer, a Democrat of New York, at a news conference.
Schumer warned Republicans who argue they support coverage for pre-existing conditions will pay a price on Election Day if they vote for Readler.
"A vote to confirm Mr. Readler is very simply an endorsement of the law suit to eliminate pre-existing conditions," he said.
Schumer was asked if he regrets that Democrats used the "nuclear option" in 2013 to lower the 60-vote threshold to break a filibuster for most judicial picks -- except those for the Supreme Court -- because it's unlikely Readler could get 60 votes right now.
"I think without question this nominee would not get on the bench," Schumer said. "The 60-vote threshold brought parties together and picked more judges to be moderate."
But he said then-Senate Majority Leader Harry Reid resorted to that rule change -- forced over the objections of Republicans -- because Republicans, led by then-Senate Minority Leader Mitch McConnell, were blocking President Barack Obama's picks to the DC Circuit Court of Appeals.
Schumer added that Senate comity was further damaged when McConnell's refused to consider Merrick Garland for the Supreme Court and when he allowed the "blue slip" tradition, which fosters bipartisan judicial picks, to wane.
McConnell, who later used the nuclear option to make it easier to confirm Supreme Court nominees, is now considering using it to speed debate of all but the most senior executive and judicial branch appointees. Schumer said he might be open to reducing debate time but only after the blue slips were restored.
This story has been updated with additional developments Tuesday.