The outcome of Tuesday’s grueling White House battle between Hillary Clinton and Donald Trump could determine how the history books remember President Obama, with his legacy on the line as one candidate vows to dismantle the outgoing president’s signature policies and the other pledges to protect his agenda.  

From ObamaCare to his court-challenged directives helping illegal immigrants to his controversial environmental regulations, the president’s initiatives and the enduring impact of his historic presidency depend in large part on the next administration and Congress.

Trump and fellow Republicans have sought since the primaries to put Obama on the ballot as much as Clinton, and returned to that theme in the final days of the race.

“Obama’s legacy is on the ballot Tuesday and the people are going to choose whether we want another four years of the same,” Ken Blackwell, former Ohio secretary of state who is on the board of numerous conservative organizations, told FoxNews.com.

Trump lately has been laser-focused on bringing down the Affordable Care Act, or ObamaCare. Rallying supporters in Grand Rapids, Mich., overnight, Trump said real change begins with repealing and replacing the law.

That message ramped up at the start of this month’s open enrollment, as Trump and running mate Mike Pence railed against the program’s rising premiums costs. Trump on Monday even claimed credit for getting the government to publish data on ObamaCare premium hikes.

In an election year marked by intra-party tensions, the health care law has been one area where the Republican Party has united, in opposition. During a radio interview Monday in Milwaukee, House Speaker Paul Ryan reiterated that if Clinton becomes president, the likelihood of wiping ObamaCare off the books becomes an afterthought.

“We actually have a plan to replace ObamaCare,” he said. “All of us have basically gotten a consensus on what our plan is, but we have to win an election to put it in place.”

Clinton countered Trump’s message Monday in Pennsylvania by touting her push to “defend the legacy of President Obama.” Clinton, if elected, may seek changes in the law to address bipartisan concern about rising premiums – but has vowed to defend it as a whole.

The legacy on the line entails far more than ObamaCare. Trump has also vowed to “cancel every unconstitutional executive action, memorandum and order” issued by Obama. This presumably is aimed largely at immigration measures. The Supreme Court already deadlocked on a case about Obama’s actions giving a deportation reprieve to millions of illegal immigrants, leaving a lower order in place that blocks it – but Trump’s immigration approach would likely signal a far tougher approach to enforcement and deportation on many fronts than Obama’s. Trump has called for cancelling all federal funding to so-called “sanctuary cities” and removing more than 2 million criminal illegal immigrants – while also suspending immigration from “terror-prone regions where vetting cannot safely occur,” a drastic change from current policy.

Another key decision on the line is the choice to fill the Supreme Court vacancy. Unless the U.S. Senate changes course and confirms Obama's nominee, appellate court judge Merrick Garland, to fill the ninth seat on the Supreme Court, whoever wins Tuesday would be responsible for selecting a justice who could cast the deciding vote in cases involving everything from climate change to transgender rights to the Second Amendment. This process, too, is a critical factor in whether Obama’s policies remain.  

Trump already has a list ready of conservative choices to fill the seat of conservative icon Antonin Scalia.

“If Donald Trump wins and has a Republican Senate, they will cement a conservative lock on the Supreme Court for at least a generation,” Gary Nordlinger, a professor in the graduate school of political management at George Washington University, told FoxNews.com. “If Hillary wins with a Democratic Senate, it could be different.”

On Friday, the Supreme Court announced it would decide whether the Obama administration can legally require public schools to allow transgender students to use bathrooms – just one hot-button issue on the docket.

In another transgender rights case, several states challenged the Obama administration’s May guidance to public schools nationwide to allow transgender students to use the bathrooms of their choice. Many conservatives have accused the Obama administration of overreach and claim it created dangerous conditions for students.

Another one of Obama’s legacy deals that faces strong criticism from both sides of the aisle is the Trans Pacific Partnership.

The giant – and semi-secretive – 12-member free-trade agreement advocated by the outgoing administration aims to deepen economic ties among the 12 nations, cutting taxes and fostering trade to boost economic growth in the process.

Trump has knocked Clinton multiple times on the campaign trail for supporting the TPP while in Obama’s Cabinet – even though she now is withholding her support. On Monday, Trump argued Clinton only got on board after she saw how many voters enthusiastically were against it.

The Republican nominee recently said in Ohio that he believes Clinton, if in a position of power, would try to pass the TPP.

During a trip to Australia in 2012, Clinton said the TTP “sets the gold standard in trade agreements to open free, transparent, fair trade, the kind of environment that has the rule of law and a level playing field.” After she left the Obama administration, Clinton’s rhetoric has shifted, but it’s unclear whether her opposition would stand if certain adjustments are made to the pact.

While key agenda items are at stake, Nordlinger argued Obama’s legacy is cemented in some regards. He credited the 44th president with stabilizing the country’s economy which was “teetering on a true economic meltdown,” and helping “improve the reputation of the United States” globally.

“While some people accuse him of being weak in international affairs, he hasn’t done anything truly stupid,” Nordlinger said. “They aren’t going to take Lincoln out of the Lincoln memorial to put him in there, but all in all, he’s been pretty darn successful.”