Heidi M. Przybyla

USA TODAY

Hillary Clinton needs all the help she can get to unite Democratic voters behind her as she closes in on the party’s presidential nomination.

Republican congressional leaders may be helping her cause with their vow to block President Obama’s Supreme Court nominee, Judge Merrick Garland.

Long before the death of Justice Antonin Scalia, Clinton was making Republican obstructionism a major focus on the campaign trail. The standoff over Garland's nomination allows Clinton to frame the election around a number of issues sacred to the party base but that also appeal to more moderate, independent voters, such immigration and abortion.

However, some of the enthusiasm among the party’s most liberal voters — many of whom are backing her rival for the Democratic nomination, Vermont Sen. Bernie Sanders — could be tempered by Obama’s pick of Garland, who is chief judge of the U.S. Court of Appeals for the District of Columbia Circuit and considered by many a moderate.

Meet Merrick Garland, Obama's SCOTUS nominee

Still, “this may be the first election where a Supreme Court appointment and future Supreme Court appointments really do change some votes,” said Evans Witt, a nonpartisan pollster at Princeton Survey Research Associates. “The Democrats will make the argument: 'Just posit Donald Trump picking a Supreme Court nominee. How does that make you feel?' ”

Michael Golden, author of the book Unlock Congress and a political science professor at Arizona State University, said the issue "is going to redound to Secretary Clinton’s benefit, first of all, because it should increase turnout and enthusiasm, but secondly it will provide her a big opportunity to campaign on a number of issues that will be before the court."

Republicans on the Senate Judiciary Committee said they would not hold a hearing with Garland, and Senate Majority Leader Mitch McConnell argues it’s important to hold off until the next president takes office “to give the people a voice.”

Five things to know about Merrick Garland

“There is not going to be a hearing or a vote with this nominee,” Sen. John Barrasso, R.Wyo., said Thursday on MSNBC. “A lame-duck president shouldn’t be making a lifetime appointment.”

On Wednesday, Clinton issued a statement calling on Republicans to “perform the Constitutional duty they swore to undertake,” noting that the Senate’s never taken more than 125 days to vote on a nominee, with the average being two months. “Evaluating and confirming a Justice to sit on this nation’s highest court should not be an exercise in political brinkmanship and partisan posturing,” she said, and the Constitution does not “make an exception to that duty in an election year.”

First Take: Obama's Supreme Court surprise

While polls show Americans relatively divided over whether the Senate should vote this year or next, a recent ABC News/Washington Post survey found three-fifths of registered voters say the Republican-led chamber should hold hearings.

Jeffrey Rosen, president of the National Constitution Center, says Clinton can make a credible obstructionism case against Republicans in Congress by pointing to the absence of hearings. “The Senate has not done this before in history. That’s not to say it’s prohibited under the Constitution,” said Rosen, a Supreme Court expert, but “this is unprecedented.”

Republicans have their own internal politics to consider, and many Senate incumbents up for re-election fear a primary threat if they disappoint their own base, which wants to stop Obama from naming any successor to Scalia.

They’re also expecting the issue to fizzle over the coming weeks and point to the 2013 Republican-driven federal government shutdown that hurt the party’s approval ratings but didn’t stop it from taking control of the Senate in 2014.

“Without much movement, it will likely disappear into the ether, swamped by Donald Trump and all the news he makes on a daily basis,” said Ron Bonjean, a Republican strategist who was a senior adviser to GOP House and Senate leaders. “I view it as a liberal base issue,” said Bonjean.

Some of the Democratic base voter outrage over GOP tactics may also be mitigated by disappointment over Obama’s pick of Garland, who’s been praised by Republicans in the past, such as Utah Sen. Orrin Hatch, and is considered by many to be moderate, said Jamal Simmons, a Democratic strategist and former Bill Clinton adviser.

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“It is something that will anger loyal Democrats, but that would have been a much more powerful argument had the president appointed someone like Loretta Lynch or another candidate that progressives would feel more strongly about,” said Simmons.

In the meantime, Clinton will use the standoff on Capitol Hill to champion some of the issues most important to Democratic voters.

She telegraphed that strategy months ago. In a January opinion piece in theBoston Globe prior to Scalia's death, she called the election a “make-or-break moment — for the court and our country.”

Republicans “see this election as an opportunity to pack the courts with jurists who will turn back the clock,” by disenfranchising unions, taking away abortion and voting rights and overruling Obama’s executive actions on immigration. She also warned of attempts by 26 state attorneys to overturn Obama’s clean-power plan.

Elections 2016 | USA TODAY Network