Republicans are greeting the Supreme Court clash expected to dominate Senate politics in the months leading to Election Day with glee, but it is filling Democrats with anxiety.

The GOP, which has been nervous about turnout, sees the prospect of a summer battle over Trump’s pick to succeed Justice Anthony Kennedy as a way to energize the base and get people to the polls.

Democrats, who had begun to feel more optimistic about November despite a difficult map that sees the party defending seats in deep Trump territory, are suddenly stuck between their voters and donors.

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Voter intensity among conservatives and liberals on the issue is expected to be high, but exactly how that plays out in Senate races in North Dakota, Montana, Indiana, Missouri and West Virginia is uncertain.

“It could have [an impact] in terms of voter turnout,” said Sen. Thom Tillis Thomas (Thom) Roland TillisThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting OVERNIGHT ENERGY: EPA head questions connection of climate change to natural disasters | Pebble Mine executives eye future expansion in recorded conversations | EPA questions science linking widely used pesticide to brain damage in children Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight MORE (R-N.C.), vice chairman of the National Republican Senatorial Committee. “It would probably produce intensity on both sides.”

Kennedy’s surprise decision to call it quits hands President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE an opportunity to significantly remake the high court, replacing a conservative justice, who occasionally sided with liberals on issues like same-sex marriage and abortion rights, with a down-the-line originalist in the mold of his first nominee, Justice Neil Gorsuch.

Democrats and liberal groups see any new replacement as a potential threat to a host of core issues, from union and worker rights to environmental protections, the Affordable Care Act, and civil and voting rights.

“I didn’t think our enthusiasm could get bigger, but the tempest is coming,” said Sen. Chris Murphy Christopher (Chris) Scott MurphyDemocratic senator calls for 'more flexible' medical supply chain to counter pandemics The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon GOP chairman to release interim report on Biden probe 'in about a week' MORE (D-Conn.).

The fight will put more of a political focus on the race for the Senate, which had been overshadowed to an extent by the battle for the House.

“Justice Kennedy’s retirement makes the issue of Senate control one of the vital issues of our time. The most important thing we can do,” President Trump said Wednesday in Fargo, N.D., where he was stumping for Rep. Kevin Cramer Kevin John CramerMomentum growing among Republicans for Supreme Court vote before Election Day On Paycheck Protection Program, streamlined forgiveness is key McConnell shores up GOP support for coronavirus package MORE (R).

Several outside groups have pledged to spend millions on advertising campaigns pressuring senators for or against an eventual nominee. That includes liberal groups that will pressure Democrats — even those in conservative states — to block Trump’s pick.

Democrats, including Sens. Joe Manchin Joseph (Joe) ManchinManchin defends Supreme Court candidate Barrett: 'It's awful to bring in religion' The Hill's Morning Report - Sponsored by Facebook - Trump, GOP allies prepare for SCOTUS nomination this week Trump meets with potential Supreme Court pick Amy Coney Barrett at White House MORE (W.Va.), Joe Donnelly Joseph (Joe) Simon DonnellyHarris faces pivotal moment with Supreme Court battle Trump meets with potential Supreme Court pick Amy Coney Barrett at White House Names to watch as Trump picks Ginsburg replacement on Supreme Court MORE (Ind.), Claire McCaskill Claire Conner McCaskillMomentum growing among Republicans for Supreme Court vote before Election Day Democratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally MORE (Mo.), Heidi Heitkamp Mary (Heidi) Kathryn HeitkampHarris faces pivotal moment with Supreme Court battle Centrists, progressives rally around Harris pick for VP 70 former senators propose bipartisan caucus for incumbents MORE (N.D.) and Jon Tester Jonathan (Jon) TesterDemocrats shoot down talk of expanding Supreme Court Pence seeks to boost Daines in critical Montana Senate race This World Suicide Prevention Day, let's recommit to protecting the lives of our veterans MORE (Mont.), have tried to show voters they are willing to work with President Trump when it benefits their state. Now, they will face cross-pressures from liberal voters and donors who will demand they take every step possible to block the court nomination.

“This becomes the defining issue in many of the closest Senate races this fall,” said Steven Law, who runs the Senate Leadership Fund, the leading Senate Republican super PAC. “For voters in deep-red states who support Trump, this will be the litmus test vote for whether you have President Trump’s back or not. Nothing else comes close.”

Asked Thursday about the coming nomination fight, several red-state Democrats demurred. Manchin refused to speculate about potential issues that would disqualify a nominee in his mind. Donnelly, who like Manchin voted to confirm Gorsuch, pledged to “look at whoever comes before us.”

Asked to comment on the open seat and the coming fight, McCaskill repeatedly declined to comment. “I’ve got nothing for you,” she said.

But McCaskill’s opponent, Missouri Attorney General Josh Hawley (R), who clerked for Chief Justice John Roberts, had plenty to say.

“The Supreme Court is the defining issue of our time. The Court makes decisions on some of the most pivotal issues in society — from the right to bear arms to religious liberty to immigration — and it is incumbent upon a United States Senator to outline what judicial philosophy they want justices to hold,” Hawley said in a statement Thursday. “Sen. McCaskill has been wrong on the last five Supreme Court nominees. Now she is ducking the question [of] what type of judge the president should nominate.”

In Indiana, where Donnelly faces former state legislator Mike Braun (R) in November, the Court fight will spur voters — specifically evangelical Christians — to the polls in levels far higher than a normal midterm, said Brian Howey, author of Howey Politics Indiana.

“Donnelly was counting on an energized [Democratic] base, but Kennedy just gassed up the evangelicals,” Howey said.

If Trump nominates Amy Coney Barrett, a judge on the 7th Circuit Court of Appeals and a Hoosier who like Donnelly graduated from Notre Dame and is one of the names on Trump’s list of potential picks, Donnelly would face added scrutiny. “This is the proverbial rock/hard place,” Howey wrote in an email.

In recent years, as Supreme Court nomination fights have become more contentious, senators who represent states that the other party’s presidential nominee carried in the previous election have become the most likely to break with their own party to support confirmations.

In the past four Supreme Court confirmation votes — for Justices Samuel Alito, Sonia Sotomayor, Elena Kagan and Gorsuch — a combined total of 21 senators from the other party voted for confirmation. Of those, 17 represented states that the other party’s president won in the previous election.

The only exceptions were Sens. Lamar Alexander Andrew (Lamar) Lamar AlexanderGraham: GOP has votes to confirm Trump's Supreme Court nominee before the election The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy This week: Supreme Court fight over Ginsburg's seat upends Congress's agenda MORE (R-Tenn.) and Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.) and former Sen. Kit Bond (R-Mo.) who voted to confirm Sotomayor. Graham also voted to confirm Kagan.

Republicans said they hoped to use the coming election to pressure Democrats into backing Trump’s pick this time, too.

“If it’s before the November election, I would expect a few Democrats to vote for the nominee,” said Sen. Roy Blunt Roy Dean BluntSocial media platforms put muscle into National Voter Registration Day Senate GOP faces pivotal moment on pick for Supreme Court This week: Supreme Court fight over Ginsburg's seat upends Congress's agenda MORE (R-Mo.).

Marc Short, the White House director of legislative affairs, said Thursday his office had reached out to red-state Democrats like Donnelly and Manchin before nominating Gorsuch. Asked whether the White House had begun reaching out to Democrats for Trump’s next nominee, he said: “I think it’s fair to draw that conclusion.”