Should Mitt Romney win the presidential election this November, one institution stands to receive a substantial makeover: the Supreme Court. The venerable justices begin a new term Monday, and it could be one of the last of its kind. During his four year term, the Republican pick for president would very likely get to nominate at least one new justice to the aging Court, a move that could drastically reshape the legal landscape for years after.

The majority of justices on the Court aren't exactly youthful. Conservative justice Anton Scalia is well into his 70s, while liberal justices Stephen Breyer and Ruth Bader Ginsburg are 74 and 79, respectively. Swing Justice Anthony Kennedy, meanwhile, is 76. Ginsburg, who has twice survived cancer, said she wants to tie the tenure of Justice Louis Brandeis, who retired in 1939 at age 82. If that happens, she'd say adieu in 2015, smack in the middle of a Romney presidency (should he win the White House.)

If Romney gets to replace Ginsburg, the ideological make up of the Supreme Court will undergo a radical shift. Right now, four reliably liberal justices face off against four even more reliably conservative justices, with Kennedy swinging between the two sides. An analysis by Geoffrey Stone, professor and former dean at the University of Chicago Law School, predicts that if Ginsburg had been replaced with a conservative justice in 2000, conservatives would have won 16 out of the 18 most important Supreme Court cases over the past 12 years, including overturning President Barack Obama's health care law.

So who might a President Romney pick for the Court? In 2007, Romney said he admired President George W. Bush's choices of Justices John Roberts and Samuel Alito, suggesting he would opt for a reliably conservative justice rather than a more middle-of-the-road one like Kennedy or former Justice Sandra Day O'Connor. "I respect legal scholars of all backgrounds, but those who are going to be on the bench, if I were lucky enough to appoint them, would be people who believe their job is to follow the law and follow the Constitution," Romney said then. During this primary season, Romney noted that he would appoint federal judges who oppose gay marriage.

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If Romney chooses an Alito-like justice to replace Justices Scalia or Thomas, he would likely face little opposition. But should he try to replace a left-leaning justice like Ginsburg with someone whose judicial philosophy strayed widely from hers, liberals might revolt. This could mean a Democratic-led endless filibustering of the nominee. Thus, Romney might have to nominate someone "whose judicial philosophy is a complete mystery" so as not to trigger filibustering from Democratic lawmakers who object to the court swinging so far to the right, says Stone.

But conservative disillusionment over losing the health care reform case just might push Romney to embrace a staunch conservative with a clear voting record, despite the messy confirmation process, says Curt Levey, the executive director of the conservative Committee for Justice advocacy group. There will be pressure for Romney to pick a "stealth" nominee--someone who has no real record--to avoid a confirmation fight, Levey says, but there may also be push back from conservatives who feel "betrayed" that Justice Roberts abandoned the court's conservative wing to uphold the health care law last summer. (Some conservatives think Roberts bowed to outside pressure, instead of deciding the case on its merits.)

"[Roberts] seemed like a conservative, but he didn't really have a record," Levey said. "And the record we all realize now maybe deserves a little more importance than we have been giving it."

UCLA School of Law Professor Adam Winkler agrees. "I think Roberts' vote will lead Republicans to be even more skeptical of judicial appointments. They're going to want even more of a clear cut history of support for conservative causes."

A short list of potential Romney selections would likely include high-profile advocate Paul Clement, who argued against Obamacare and for Arizona's immigration law in front of the Supreme Court this year; Viet Dinh, a former lawyer in the Bush administration; and Miguel Estrada, a lawyer and former Bush nominee to the Circuit Court whom Democrats filibustered in 2001. D.C. Circuit judge Brett Kavanaugh, a Bush appointee, is also talked about as a likely Republican choice, along with Diane Sykes, a judge on the 7th Circuit.

Clement's penchant for choosing tough, controversial cases indicates that he would be consistently conservative on the court, and not influenced by outside pressure on big cases, said Levey. Clement resigned his position as partner at a law firm when groups criticized him for agreeing to defend the federal Defense of Marriage Act after the federal government decided it was unconstitutional.

"Paul Clement has been on the top of everyone's list now for some years and he could easily just sit back and take non controversial cases in order to take his best chance of being confirmed," Levey said. "He's not doing that; he's taking the most controversial cases."

But Winkler of UCLA disagrees, noting that Clement's record on gun rights when he was President George W. Bush's solicitor general might stymie his chances with conservatives. Clement argued that a circuit court's decision to strike down Washington D.C.'s ban on handguns should be revisited, which placed Clement at odds with then-Vice President Dick Cheney and other conservatives.

"Clement took a position that was seen as a betrayal," Winkler says. "That's one of the hurdles he'll have to overcome. I think that could be a sticking point."

If Ginsburg is replaced with a justice who has a much more conservative judicial philosophy, the court's three remaining liberals would find themselves without much hope for a majority, and swing-justice Kennedy's decisions would no longer reliably change the outcome of cases. It's possible that Roe v. Wade would be overturned, and other areas of the law would also be transformed.

The liberal justices would "start writing for history," Winkler says, in place of writing actual law.