Shortly after Donald Trump won the presidency in 2016, Obama tried warning him: Go through Congress — as laws are more difficult for future administrations to overturn.

Trump discarded Obama's advice, even after he had attacked Obama for using executive authority on immigration in 2014, accusing him of trying "to subvert the Constitution."

Trump has latched onto executive power to press his conservative agenda on immigration and the environment among other areas, repeatedly crossing boundaries that his predecessors did not.

But in wielding this type of power, he's also building a flimsy foundation that could quickly be unraveled if a Democrat wins next year's presidential race.

Many of his own decisions cracking down on immigration could be reversed, as well as broad efforts to roll back Obama-era rules safeguarding the environment.

"If the president were not to be re-elected in 2020, I think you would have a lot of opportunity to turn back the policy changes he's proposed," Andrew Rudalevige, a professor of government and scholar of the presidency at Bowdoin College, told Insider.

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President Barack Obama came into office in 2009 with deep misgivings over his predecessor George W. Bush's expansive use of executive power, particularly in national security. He sought to chart an alternate course early on as a result, promising to work with Republicans and foster a new spirit of bipartisanship.

By his second term, however, Obama was relying more on his "pen and phone" — his metaphor to describe the executive authority he once scorned. Faced with a lack of cooperation from Republicans in Congress, Obama embraced his executive powers as a governing tool to rescue his stalled domestic agenda, especially in strengthening environmental protections and extending equal rights to minorities.

But shortly after Donald Trump won the presidency in 2016, Obama tried warning him: Go through Congress — as laws are more difficult for future administrations to overturn.

"My suggestion to the president-elect is, you know, going through the legislative process is always better, in part because it's harder to undo," Obama told NPR.

Read more: Trump's 2014 comments criticizing Obama for taking executive action 'because he is unable to negotiate w/ Congress' are coming back to haunt him

Trump has discarded Obama's advice, despite having attacked Obama as trying to "subvert the Constitution" for using executive authority on immigration in 2014.

Trump latched onto executive power to press his conservative agenda on immigration and the environment among other areas, repeatedly crossing boundaries that his predecessors did not. Trump has been a political wrecking ball, reversing at least 15 of Obama's initiatives and highlighting the shakier elements of his predecessor's legacy.

But in wielding a similar type of power, Trump is also building a flimsy foundation that could quickly be unraveled if a Democrat wins next year's presidential race. Many of his own decisions cracking down on immigration could be reversed, as well as broad efforts to roll back Obama-era rules safeguarding the environment.

"If the president were not to be re-elected in 2020, I think you would have a lot of opportunity to turn back the policy changes he's proposed," Andrew Rudalevige, a professor of government and scholar of the presidency at Bowdoin College, told Insider.

Many of those drastic changes that have emerged from Trump's executive branch have partially been the product of a polarized Congress.

Congress has ceded authority to the executive branch, making it easy for presidents to go around lawmakers.

The use of executive power has dramatically expanded under both Republican and Democratic presidents in the last eight decades — and Congress has essentially ceded much power to the White House when it comes to lawmaking as its become more gridlocked. Rudalevige called it "almost a dereliction of duty."

"We've had a period where Congress has delegated a huge amount of authority to the executive branch," he says. "A lot of this is tied up the rise of partisan polarization. It is very difficult for members of Congress to work across party lines to do the kind of compromising they used to do routinely."

Read more: Trump and congressional Democrats are taking Washington gridlock to a whole new level

The Pew Research Center found that while the GOP-led 115th Congress passed the most laws in a decade, they weren't more substantive — and the government shut down once over funding for Trump's proposed border wall.

Only two major laws have been passed in Trump's presidency so far: the 2017 Republican tax cuts and a bipartisan criminal justice reform signed into law earlier this year, a sparse legislative record for a GOP president who once had a party majority in both the House and Senate. And Trump's efforts to repeal and replace the Affordable Care Act reached a dead end early on.

U.S. President Donald Trump celebrates with Congressional Republicans after the U.S. Congress passed sweeping tax overhaul legislation, on the South Lawn of the White House in Washington. Reuters/Carlos Barria

"You'd expect a president with a working majority of his own party in Congress to do more legislatively than the Republicans achieved in 2017 and 2018," Rudalevige told Insider. His difficulties then stemmed in part from Democratic senators use of the filibuster to block legislation.

However, Trump has been incredibly successful in his drive to reshape the federal judiciary. He's appointed judges at a record pace compared to past presidents, and given the appointments are for life, it could thrust the ideology of the courts to the right for generations on issues like abortion rights, according to the Los Angeles Times.

With Democrats now controlling the House after the 2018 midterms, though, there is little prospect Trump will be able to muster the bipartisan consensus needed to pass more major legislation. And he's turning to executive authority to bolster his political record ahead of 2020.

"The president obviously wants a record to run on in 2020 and that's not going to be a legislative record at this point. It's got to be one driven by administrative action," Rudalevige says.

Read more: The 2020 presidential election could come down to college students and that could be trouble for Trump

Since taking office, Trump has infused his executive authority with a bit of showmanship, holding elaborate signing ceremonies as an opportunity to flaunt his administration's regulatory moves. But a review from the Los Angeles Times of 101 executive orders Trump signed since inauguration day found that few altered policy in a significant way — many had instead created task forces or otherwise demanded enforcement of laws already on the books.

"You don't really need an executive order for a lot of this stuff, but it makes for a good show," Elaine Kamarck, director for the Center of Effective Public Management at the Brookings Institute, told the Los Angeles Times. "He even gives out pens, which is really sort of ridiculous."

Ahead of the 2020 election, a 'tremendous amount of activity with mixed results.'

Many of Trump's policies have met resistance in the courts, especially on the environment and immigration. The latter has been a priority for the president, and he's moved aggressively to deport undocumented immigrants and drastically limit legal immigration into the US.

"What we've seen in this administration is far more extensive than anything that was done in the prior administration," Doris Meissner, a Clinton administration veteran who is now the Director of the US Immigration Policy Program at the Migration Policy Institute, told Insider.

"There's been a tremendous amount of activity but with mixed results," Meissner says, noting the administration's initial rashness in crafting and implementing immigration policy undercut their effectiveness. But she says Trump officials are learning from their mistakes.

After a yearlong review process, the Trump administration recently announced a new rule to be implemented in October barring immigrants deemed likely to receive public benefits from receiving their green card. And it's also pushing to open the door to the indefinite detention of migrant children and their families near the border. Immigration advocates, however, have promised to fight both measures in court.

Read more: The Trump administration's new green-card rule could be 'a backdoor' to immigration reform, experts say

The administration admitted the lowest number of refugees since the refugee program was created in 1980. However, Meissner says it's a policy that a Democratic administration could easily reverse.

Other moves are likely more permanent, such as Trump's decision to pull out of the Trans-Pacific Partnership, according to The Atlantic.

Many of the Democratic presidential candidates have pledged they would reverse many of Trump's orders in their first 100 days in office — his decision to pull out of the Paris climate agreement has drawn their ire, and nearly all the Democrats running have said their administrations would rejoin it.

During the 2016 campaign, Trump vowed to "cancel every unconstitutional executive action, memorandum and order issued by President Obama." As many of his policies haven't been made law, Trump may very well find his own legacy assaulted by a future Democratic administration should he be defeated in 2020.