WASHINGTON — Conservatives are betting this week’s Senate vote on Supreme Court nominee Neil Gorsuch will cause Democrats up for re-election in 2018 to weigh last November’s election results in deciding whether to support him or not.

They are targeting Democrats — such as Sen. Joe Donnelly of Indiana and Sen. Claire McCaskill of Missouri — from states President Donald Trump won easily, predicting political consequences if they vote against his high court nominee.

Donnelly, who seeks a second term next year, announced Sunday he will support Gorsuch but wants him subject to the Senate’s 60-vote threshold for Supreme Court nominees. He said Gorsuch is “a qualified jurist who will base his decisions” on his understanding of the law.

He joined two other Democratic senators facing re-election next year in pro-Trump states — West Virginia’s Joe Manchin and North Dakota’s Heidi Heitkamp — who have now announced they will support Gorsuch.

But Missouri’s McCaskill said Friday she will not back Gorsuch despite the political risk. She also said she expects Republicans will succeed in modifying the Senate 60-vote filibuster rule to a simple majority vote, and the change “will usher in more extreme judges in the future” on the Supreme Court.

Gorsuch, a federal appeals court judge from Colorado, needs at least eight Democrats to support him to reach the 60 votes necessary to stop a Democratic Senate filibuster, known as cloture, against his appointment.

Republicans hold a 52-48 edge over Democrats in the Senate. Thus GOP senators can change the rules to require a simple majority vote to block a filibuster and confirm Gorsuch — an action known as the “nuclear option.”

Democrats, when they controlled the Senate, changed the rules and used the option to overcome Republican objections to federal judges below the Supreme Court level.

Senate Majority Leader Mitch McConnell of Kentucky said on NBC’s “Meet the Press” Sunday he hopes it is not necessary to invoke the nuclear option on Gorsuch’s nomination but Democrats can blame themselves if Republicans do so.

“Neil Gorsuch will be confirmed this week,” said McConnell. “How that happens will depend on our Democratic friends; how many of them are willing to oppose cloture on a partisan basis to kill a Supreme Court nominee. It has never happened before in the history of the country.”

Sen. Chuck Schumer of New York, the top Senate Democrat, appearing on the same NBC program, said it’s “highly unlikely” Gorsuch has enough votes to win confirmation under the 60-vote cloture rule because of his support from hard-right groups.

He urged Trump to withdraw the Gorsuch nomination and confer with Republican and Democratic leaders to come up with a mainstream Supreme Court nominee.

“Our Republican friends are acting like a cat on the top of a tree, and they have to jump off, with all the damage that entails,” said Schumer. “Come off the tree and sit down with us and we will produce a mainstream candidate. A Republican.”

The conservative Judicial Crisis Network, which helped block President Barack Obama’s nominee Merrick Garland last year, has been airing costly TV and radio ads in Indiana, Missouri and other pro-Trump states for Gorsuch.

In January, the network announced it had committed $10 million to pressure vulnerable Democratic senators to break ranks with their party leaders and confirm Gorsuch.

Network policy director Carrie Severino mentioned Donnelly and McCaskill in particular — and $1 million in ads have been running in their states and two others where Democrats face re-election in 2018. 

She said the ads “will force vulnerable senators up for re-election…to decide between keeping their Senate seats or following Chuck Schumer’s liberal, obstructionist agenda.”

Kery Murakami is CNHI’s Washington reporter. Contact him at kmurakami@cnhi.com.