For the first two hours after President-elect Trump takes the oath of office on Jan. 20, he will toast his inauguration with a lavish lunch and celebratory parade down Pennsylvania Avenue. But President Trump will probably fill the rest of his first 24 hours in office beginning to demolish his predecessor's legacy, which he has promised to reverse almost completely once he is sworn in on the steps of the U.S. Capitol.

Trump has already signaled that Day One of his presidency will be activistic in its agenda and energetic in its execution. The president-elect has cut short the time he will spend watching the customary parade and pared down the number of inaugural balls he will attend with his wife, Melania, who will then be first lady.

His transition team says that while Trump is happy to observe many of the historic traditions surrounding presidential inaugurations, he also wants a rapid start on his promise to "Make America Great Again."

"Traditionally, there's a lot of celebratory action on Day One," Sean Spicer, incoming White House press secretary, told the Washington Examiner. "I think there's going to be plenty of that."

Spicer suggested, however, that Trump will dedicate much of his first 24 hours in office taking action on policy as well.

"He is eager to get to work, and I think you're going to see a flurry of activity that afternoon, Saturday, Sunday and Monday," Spicer said.

President Obama, for his part, has spent his final days in office trying to set as much of his legacy in place as possible with the glue of executive orders, foreign policy overtures and so-called midnight regulations. Each is intended to create new obstacles for Trump either to overcome or resign himself to as his presidency begins. Many of Obama's eleventh-hour maneuvers, such as increasing sanctions against Russia and designating large swaths of western land as federal parks, could tempt Trump into dedicating part of his first day to rolling back what was put in place only after he won his election campaign.

"Most of the literature on presidential transitions asserts that the real effective political power of the outgoing administration declines the closer you get to Inauguration Day and therefore the more necessary it is for the outgoing administration to consult with the incoming administration and try to arrive at a shared policy," said David Clinton, an expert in presidential transitions at Baylor University.

"President Obama seems to be leaning on the side of less in the way of consultation and more on the side of insisting that the power and the responsibility and the right to make decisions all continues to reside with him right up until the last minutes," Clinton added.

Obama and Trump have tussled over policy in the run-up to Inauguration Day.

Trump promised swift changes to American participation in the United Nations in late December after Obama broke with decades-old policy and allowed the U.N. Security Council to pass a resolution that will make it easier for Israel's enemies to attack the Middle East's only democracy.

Trump and Obama have repeatedly sparred over policy toward Russia. Obama issued a rash of sanctions against Russians suspected of orchestrating election-related cyberattacks on Democrats between Christmas and New Year, throwing dozens of Russian diplomats and their families out of the country. Trump, meanwhile, exchanged Christmas cards with Russian President Vladimir Putin and stood by his campaign promise to thaw relations with Moscow.

Thanks to Obama's last-minute hyperactivity, Trump could face a choice between filling his first day with new policies or spending it on the destruction of old ones.

"A lot of his time on that first day will probably be spent not so much on his new initiatives as in undoing things that his predecessor has done, or at least starting the process for undoing them," Clinton said.

Clinton, who co-authored a book called Presidential Transitions and Foreign Affairs, said the reversal of some Obama policies could stall due to legal challenges that would create delays.

"Some of those will likely get tied up in court," Clinton said of swift orders Trump might issue to roll back Obama's actions.

"If he challenges this expansion of environmentally-protected federal lands, which is another initiative of President Obama, that will no doubt be challenged in court," Clinton said. "He may want to fight that fight. He could start it in the first 24 hours, but he couldn't accomplish it in the first 24 hours."

Trump's policy promises have gone far beyond his pledge to undo the Obama agenda. He has vowed to replace it with a business-friendly blueprint for getting the country back to work, describing himself on the campaign trail as "the greatest jobs president God ever created."

Mark Serrano, a Republican strategist who worked on President Reagan's inauguration committee, said Trump should remember the premium he placed on job creation when deciding what to tackle on Day One at the White House.

"I think if you consider, in his first 24 hours, the most important symbolic things he does should be related to, most importantly, jobs and the economy, because that's first and foremost what got him elected," Serrano said.

Trump has already hinted that much of his energy on Jan. 20 will be dedicated to policies that boost jobs creation. In a video address released shortly after his election victory, Trump previewed the six-point plan he would follow on his first day at 1600 Pennsylvania Ave.

"I've asked my transition team to develop a list of executive actions we can take on day one to restore our laws and bring back our jobs," Trump said. The list included a five-year lobbying ban and a notification of intent to withdraw from the Trans-Pacific Partnership.

The president-elect promised to "cancel job-killing restrictions on the production of American energy" immediately upon entering the Oval Office.

Serrano said Obama's ambitious pursuit of his agenda, often without the help of Congress, could leave many of his policies vulnerable to Trump's pen.

"Look at the Obama legacy this way: since the Democrats lost the House in 2010, for six years, we have lived with gridlock ... and I say that's a success on the part of Republicans for blocking the Obama agenda," Serrano said. "That's why the Obama legacy will prove to be ephemeral, because only laws and statutes have a lasting effect. ... His executive orders can be rolled back."

What's more, Serrano said, Trump could quickly instruct his Cabinet agencies to begin searching for spending cuts and ways to scale back federal regulations issued under by Obama. By focusing on policies enacted with executive orders and regulatory changes, Trump could immediately start chiseling away at the Obama legacy he fought so hard to remove.

"All of that erasing," Serrano said, "will take place in the first 24 hours."