Hillary Clinton on Monday turned the Supreme Court vacancy  into a campaign topic, saying it is “one of the most important issues facing the country” and arguing the next president will have a major impact on the high court.

The Democratic presidential candidate warned a crowd at the University of Wisconsin about the future of the court -- which rules on the country’s most important legal issues -- if Republican front-runner Donald Trump becomes president.

“What kind of justice would President Trump appoint?” Clinton asked before pointing out Trump’s call for a temporary ban on Muslim immigrants amid fears of domestic terrorism and his opposition to granting amnesty to 11 million illegal immigrants now in the U.S.

Clinton opened a two-day campaign trip to Wisconsin ahead of the state's April 5 primary with a reference to President Obama's nomination of Judge Merrick Garland to the highest court --a topic certain to unite Democrats, whether they support her or her primary rival, Vermont Sen. Bernie Sanders.

“There are so many challenges that we need to take the time for, those that don’t get attention on the campaign trail,” said Clinton, who is less popular than Sanders among young, college-age voters.

Senate Majority Leader Mitch McConnell and others in his leadership team have said that a replacement for Justice Antonin Scalia should be nominated by a new president, not one with nine months left in office.

But Clinton argued it was reminiscent of GOP-led gridlock that stymied Obama's two terms.

"We chose a president. We chose him twice," Clinton said. "And now Republicans in the Senate are acting like our votes didn't count and President Obama is not still our nation's leader."

She called on Senate Judiciary Chairman Sen. Charles Grassley, R-Iowa, to commit to giving Garland a hearing.

And she rebuked Wisconsin Sen. Ron Johnson, who is among the Republicans blocking the Garland nomination and facing a tough re-election bid.

"Tell him to stop playing games with the Supreme Court," Clinton said, noting Johnson's 2016 challenge from former Democratic Sen. Russ Feingold.

Grassley, speaking ahead of Clinton's remarks, said she was trying to divert attention from her "email troubles," refererring to probes into her use of a private email system as secretary of state.

"This is simply a blatant attempt by Secretary Clinton to politicize the Supreme Court and to change the conversation," Grassley said in a statement. "Her actions as secretary of state are under investigation by Congress, two Obama-appointed inspectors general, and the FBI."

Republican National Committee spokesman Michael Short said, “The only reason Hillary Clinton is calling on Republicans to breach decades of bipartisan precedent of not confirming election-year Supreme Court nominees is so she could have a liberal majority on the Court to help her carry on President Obama’s legacy of executive overreach if elected.”

Clinton holds a large lead among delegates against Sanders, but is trying to stamp out the senator's momentum following his victories in five of the last six states holding contests.

“So I hope you and everybody across Wisconsin keep the court in mind when you vote,” Clinton said Monday. “I will keep advocating and talking about it and calling on the Senate to do its job.”

Sanders was also campaigning in the state this week and has identified upcoming contests in Wisconsin, New York and Pennsylvania as states where he could cut into Clinton's delegate lead.

The Associated Press contributed to this report.