Senator Claire McCaskill said she will join the Democrats attempted filibuster of Supreme Court nominee Neil Gorsuch and will not vote for him, making it almost certain that Republicans will have to trigger the “nuclear option” to confirm President Trump’s first Supreme Court nominee.

The Missouri Democrat announced Friday in a post on Medium, faulting the nominee for “a stunning lack of humanity.”

“While I have come to the conclusion that I can’t support Neil Gorsuch for the Supreme Court ?- ?and will vote no on the procedural vote and his confirmation? – ?I remain very worried about our polarized politics and what the future will bring, since I’m certain we will have a Senate rule change that will usher in more extreme judges in the future,” McCaskill wrote in a post on Medium.

She said the nomination of Gorsuch goes against the grain of Trump’s promise to help working-class Americans because he is “a judge who can’t even see them.” McCaskill also raised concerns about Gorsuch’s refusal during his confirmation hearing to say how he viewed the constitutionality of campaign fundraising regulations, which were limited by the landmark case Citizens United v. Federal Election Commission in 2010.

“I cannot support Judge Gorsuch because a study of his opinions reveal a rigid ideology that always puts the little guy under the boot of corporations,” she said adding “I cannot and will not support a nominee that allows dark and dirty anonymous money to continue to flood unchecked into our elections.”

What makes McCaskill’s opposition unique is that she is the first Democrat facing reelection next year in a state President Trump carried by double digits to come out against Gorsuch, a move which will likely force other “on the fence” Democrats to follow in her footsteps.

The political press is divided over what her no vote means: according to Axios: “Gorsuch just got the last “no” it needed so the Democrats can meet the vote threshold to filibuster his nomination. Republicans will now have to get rid of the 60-vote filibuster threshold for judges, or allow Gorsuch’s nomination to fail.”

A less definitive conclusion comes from the Hill, according to which her “no” vote shrinks the pool of Democrats who have undecided or unclear positions on Gorsuch to nine. Gorsuch’s nomination needs the backing of eight Democrats or Independents, along with all 52 Republicans, to break a filibuster.

Only two Democrats have so far said they will vote to end a filibuster of Gorsuch and support his final confirmation, according to The Hill’s Whip List. Both of them, Sens. Joe Manchin (W.Va.) and Heidi Heitkamp (N.D.), represent states Trump won overwhelmingly in November.

Meanwhile, Senate Leader Mitch McConnell has vowed that Gorsuch will be confirmed and has told colleagues to expect a vote to change the rules to lower the threshold for ending a filibuster to a simple majority, i.e. the “nuclear option”.

As The Hill adds, to avoid a showdown over the rules, it now becomes crucial for Gorsuch to pick up the support of the two remaining undecided Democrats who face reelection next year in strongly pro-Trump states: Sen. Jon Tester (Mont.) and Sen. Joe Donnelly (Ind.).

Gorsuch would likely also need the support of senior Democrats such as Sen. Dianne Feinstein (Calif.), the ranking member on the Judiciary Committee, and Sen. Patrick Leahy (Vt.), who might be concerned about preserving their power to filibuster for the next vacancy on the court.

Other Democrats up in the air are centrist Sens. Mark Warner (Va.) and Chris Coons (Del.), along with Independent Sen. Angus King (Maine), who praised Gorsuch earlier this year as “exceedingly independent.”

Assuming Axios’ whip list is the correct one, and McCaskill’s vote was the tiebreaker, forcing the “nuclear option”, the likely outcome is to make the already deep split between Republicans and Democrats even more polarized, further complicating the passage of any future Trump legislative proposals.