Washington (AFP) - Transitioning from businessman to politician has been tough for Donald Trump.

The billionaire dealmaker promised sweeping-change-made-easy as president, but now finds himself facing fierce opposition in the Congress and the courts.

It's a basic civics lesson most school kids know by heart but one that Trump has had to re-learn the hard way: under the US Constitution, the power of the president is checked by the legislative and judicial branches.

Those checks and balances have caused the first-time politician major setbacks to his two biggest initiatives to date, his travel ban and his attempt to overhaul the health care system.

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"Our presidency is very weak in terms of the ability to set the legislative agenda" compared to those of other democracies, Dartmouth government professor John Carey says.

The White House can't introduce bills to Congress, for instance. That's the prerogative of legislators, who set their own agenda.

The opposition party's rights remain especially important in the Senate, where a qualified majority of 60 of 100 votes is required to pass a number of measures, including most tax and spending bills.

"The president's power in terms of compelling legislators is mainly a power of persuasion," Carey says. "And there, Trump severely overestimated his ability."

The US president's opponents also typically rely on the judicial system to oppose his decisions and sometimes successfully block them.

That's nothing new. The Supreme Court almost sank many provisions of Franklin Roosevelt's New Deal in the 1930s. But the "judicialization" of American politics has intensified in recent years.

"I can't remember any president so much challenged in the courts so soon," the constitutional scholar Erwin Chemerinsky said.

Those challenges are taking place in one of the most polarized contexts in history, with Trump lashing out against what he calls a politicized justice system, accusing it of encroaching on presidential powers that he is discovering are far less absolute than he imagined.

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- The system pushes back -

The particular characteristics of Trump's presidency are amplifying the usual strains present under the constitutional separation of powers.

He's the most unpopular head of state in recent history at this point in his presidency, with an approval rating of just over 40 percent. The Democrats in Congress -- who worked together with the popular Ronald Reagan in 1981 and other Republican presidents when they held the majority -- have very little incentive to compromise with the current leader.

Even members of Trump's own majority Republican Party are defying him.

It was the hard-line conservative faction known as the Freedom Caucus that sank his effort to repeal Obamacare last week, a manifestation of a long-running internecine battle within the party.

The unorthodox, impatient management style of a businessman with little apparent desire to steep himself in the details -- or sometimes even the major points -- of policy has increased the rancor and chaos in Washington.

Having promised to "drain the swamp" of corruption in the capital, Trump has also surrounded himself with billionaires and ultra-conservatives with a record of fierce ideological opposition to government but precious little experience in the political system's actual functioning.

"This is the worst start for a presidency in my lifetime," Duke political science professor David Rohde said.

- Not all lost -

Still, at just 10 weeks into his first term, the 45th president retains prerogatives that, if used wisely, could enable him to regain the upper hand, including in a looming battle over the federal budget.

His predecessors George W. Bush and Barack Obama learned to work around congressional obstruction and paralysis when possible by using their authority to enact executive orders. Although some of their initiatives ultimately failed, others have lasted.

"There's still plenty of opportunity for Trump to take really consequential action on policy through executive orders and through the regulatory process," Carey said, pointing to Trump's decision not to "waste any time" this week by rolling back Obama-era environmental protections immediately following his health care defeat last week.

As for the judicial system, Trump will have opportunities to put his mark on it, starting with his nomination of Neil Gorsuch to a seat on the Supreme Court, which the Republican majority in Congress is poised to approve.

Over the longer term, all the federal judges the president appoints will gradually influence the court system's political makeup.

"It would take many years," Chicago Law School professor Eric Posner says. However, "if he serves out two terms, he probably will have appointed a substantial minority of all the federal judges."

Thanks to the advancing ages of many judges sitting on appeals court benches, Trump may be able to appoint between a third and half of appellate judges, which would put a major stamp on the country's judicial system.