Republican presidential candidate Donald Trump speaks at Trump Tower in New York, May 3, 2016. Reuters/Lucas Jackson

With Donald Trump becoming the presumptive Republican presidential nominee this week, the prospect of the billionaire businessman choosing the next Supreme Court justice got a lot more real — and that's got to scare both Democrats and Republicans.

Trump has supported Senate Republicans in their refusal to consider President Barack Obama’s nominee, saying he agrees that the next president should fill the spot left by Justice Antonin Scalia’s death. But when asked who he thinks should be the next Supreme Court justice, Trump has made a mixture of comments about general qualities he’d like to see, giving limited insight into his thinking on the matter.

After saying last year that he might appoint his sister, a respected federal judge, to the Supreme Court and then claiming that was a joke, Trump named two federal judges he'd consider, both appointed by President George W. Bush. Judge Diane Sykes and Judge Bill Pryor, Trump’s two suggestions, both have very conservative records — Pryor once called the landmark 1973 abortion case Roe v. Wade “a constitutional right to murder an unborn child” and Sykes has ruled to expand religious employers’ rights to deny birth control coverage to employees.

“The idea would be Scalia reincarnated,” Trump told conservative radio host Hugh Hewitt in March about his potential Supreme Court pick.

Trump said back in December that Chief Justice John Roberts “let us down” by turning aside lawsuits seeking to get rid of the Affordable Care Act, and added that his current favorite Supreme Court justice is Clarence Thomas. The prospect of Trump naming a conservative justice like Thomas terrifies Democrats because right now the Supreme Court is balanced with four liberal and four conservative justices. In recent years when Antonin Scalia was on the court (he died in February), Justice Anthony Roberts had been the deciding vote in cases when the other justices split 4-4 along ideological lines, but he is still largely a conservative.

There are a number of big issues in front of the Supreme Court this year, including affirmative action, Obama's immigration executive actions and restrictions on abortion providers, and with only eight justices these topics could get revisted another time. Democrats want a majority of liberal judges on the bench to set it up for more-likely favorable rulings on those issues and others.

Beyond Trump's preference for Thomas, a longtime foe of liberals, the candidate made an even bigger nod to conservatives when he said he received help from the conservative Heritage Foundation in compiling a list of “seven to 10” justices he would consider for the high court.

“We're going to have a conservative, very good group of judges,” Trump said during a press conference in late March. “I'm going to submit a list of justices, potential justices of the United States Supreme Court, that I will appoint, from the list — I won't go beyond that list. I'm going to let people know, because some people say maybe I'll appoint a liberal judge. I'm not appointing a liberal judge.”

By “some people” Trump was likely referring to his former rival Texas Sen. Ted Cruz, who repeatedly warned that the New York billionaire could not be trusted to appoint a conservative justice to the high court. Cruz even created an attack ad specifically about the issue before he dropped out of the presidential race this week.

In the ad, the words “Life,” “marriage,” “religious liberty” and “the Second Amendment” float on the screen before a narrator says, “We’re just one Supreme Court justice away from losing them all.” It shows an old interview of Trump proclaiming he is “very pro-choice” before the narrator returns to say, “We cannot trust Donald Trump with these serious decisions.”

Other Republicans have expressed doubts about Trump's conservative leanings, and now that he is the nominee, there are increasing rumblings that Senate Republicans might want to rethink their opposition to Obama’s choice Merrick Garland, a moderate who many have said is extremely qualified. The conservative blog RedState wrote a piece urging the GOP to confirm Garland "ASAP" to avoid worrying about Trump's choice.

When Scalia died in February, Senate Republicans announced within hours that the next president should choose the Supreme Court nominee, but now that the next president could be Trump, GOP lawmakers are finding themselves in a difficult position. For some Republican senators facing tight reelection races this fall, they are particularly reluctant to embrace Trump because his comments on women, Muslims and immigrants have drawn rebukes from those crucial voting blocs.

Not only are some Republicans unsure what kind of justice Trump will pick for the court, but he has also frequently shown he believes in conspiracy theories and demonstrated a lack of basic understanding of how certain aspects of the U.S. legal system work. During a presidential primary debate, he seemed to say that judges sign bills, he has misunderstood key aspects of Roe v. Wade and said he hopes the decision gets “unpassed.”

Several Senate Republicans declined Thursday to tell The Hill whether they would prefer Trump fill the Supreme Court vacancy over Obama.

“I’m not going to answer that question,” Sen. Dean Heller of Nevada about who he trusted more to make the decision. Sen. Jeff Flake of Arizona said, “I wouldn’t want to rank it,” and Sen. Mike Crapo of Idaho said, “I’m not going to get into it,” according to The Hill.

Under normal circumstances, the refusal of Republican Senators to say they’d prefer their own party’s nominee to choose the next Supreme Court justice would be shocking. But with Trump as the nominee, it’s yet another sign that he scares politicians on both sides of the aisle.

He has promised to get more “presidential” once he becomes the official nominee, so there is a chance Trump will make his stance more clear come this summer. But for now, both sides are left wondering whether Trump will keep his promises and unsure of how terrified they need to be.