WASHINGTON (Reuters) - It may soon become difficult to determine who sits in the hotter seat: U.S. President Donald Trump’s Supreme Court nominee Brett Kavanaugh or Senate Democrats from conservative states who must decide whether they are jeopardizing their political careers by opposing him.

Supreme Court nominee Judge Brett Kavanaugh speaks in the East Room of the White House in Washington, U.S., July 9, 2018. REUTERS/Jim Bourg

Trump, a Republican, named Kavanaugh, a federal appeals court judge from Washington, to the highest court on Monday, setting the stage for a political fight that could consume the weeks before the congressional elections in November.

Conservative advocacy groups are ready to pressure five moderate Senate Democrats to support Kavanaugh, all of whom are up for reelection in states that overwhelmingly backed Trump in his presidential run. They argue that not doing so will damage the senators politically.

The Senate must confirm Trump’s nominee by a majority vote. The president’s party holds 51 of 100 Senate seats, so liberal groups will apply pressure on those same Democrats to hold firm against Kavanaugh because the loss of only a Republican vote or two could sink the nomination.

“They are stuck between a rock and a hard place,” said Ford O’Connell, a Republican strategist.

Three of those largely rural state Democrats, Joe Donnelly of Indiana, Heidi Heitkamp of North Dakota, and Joe Manchin of West Virginia, voted to confirm Trump’s previous Supreme Court nominee, Neil Gorsuch, last year. All three have touted their ability to work with Trump on various issues.

The other two Democrats in so-called red states that lean Republican, Claire McCaskill of Missouri and Jon Tester of Montana, are also at risk of losing their seats.

“Obstructing confirmation will only backfire on vulnerable red-state Democrats and show voters that all their talk of bipartisanship is nothing but hot air,” Katie Martin, communications director for the National Republican Senatorial Committee, which backs Republican Senate candidates, told Reuters.

To that end, the Judicial Crisis Network, which pushes for conservative judicial nominees, will launch a $1.4 million ad campaign targeting Donnelly, Heitkamp, and Manchin, according to a representative for the group.

POLITICAL DYNAMIC

Americans for Prosperity, a conservative policy advocacy group backed by the influential Koch network, has planned a seven-figure ad campaign to support Kavanaugh, as it did last year on behalf of Gorsuch, as well as mounting a grassroots campaign in Indiana, North Dakota, and West Virginia.

Trump himself has been keenly aware of the political dynamic involved. The White House invited on Monday several vulnerable Democratic senators to the event naming Kavanaugh in order to place maximum pressure on their vote. Each declined.

As a counterweight, a new liberal interest group, Demand Justice, plans to spend as much as $5 million to push the moderate Democrats to hold fast against the nominee, as well as attempt to persuade moderate Republican senators Susan Collins of Maine and Lisa Murkowski of Alaska to oppose Kavanaugh.

Democrats have another reason to worry about the impact of the Supreme Court nomination, said Stuart Rothenberg, a non-partisan political analyst in Washington. The red-state senators’ support for Kavanaugh could dampen the Democratic Party’s anti-Trump enthusiasm and, as a result, reduce voter turnout in the congressional elections.

Still, Chris Kofinis, a Democratic strategist and former top aide to Manchin, warned that Democratic leaders such as Senate Minority Leader Chuck Schumer should not force at-risk Democrats to oppose Kavanaugh if it isn’t in their best interests. “They have to speak for themselves,” he said.

While Collins, Murkowski and Donnelly were non-committal on Monday night, Manchin spoke up after Trump’s pick was announced.

He said on Twitter he would decide whether to support Kavanaugh based on whether the nominee would vote to invalidate sections of the Affordable Care Act, which guarantees insurance coverage for people with pre-existing medical conditions.