Washington (AFP) - He may be a new kind of president, employing a go-it-alone business style while upending White House norms, but Donald Trump now confronts a venerable US system of checks and balances.
Trump has moved with lightning speed on multiple fronts since taking office January 20, acting to roll back regulations on industry, freeze federal hiring, and dismantle his predecessor's health care reforms.
But his most high-profile move -- summarily banning the entry of refugees and people from seven predominantly Muslim countries -- ran aground Friday in the US courts.
A federal judge temporarily suspended his executive order, and a US court of appeals in San Francisco turned down -- at least for now -- an administration request that the judge be overruled.
Travelers who had been banned were again trickling back into the country.
- Limits on presidential power -
The clash is schooling Trump on the limits of presidential reach in a democratic system in which power is divided among the three branches of government: executive, legislative and judicial.
Democrats have accused Trump, who declared last July that "I alone can fix it," of acting like an autocrat.
"We're a democracy, not a one-man show," warned liberal Senator Bernie Sanders on Sunday. "We are not another Trump enterprise."
The writers of the US Constitution devised safeguards against dictatorial abuses of power, namely the courts and Congress.
"So far a case can be made that the checks and balances system is working the way it was intended to," Robert Shapiro, a political science professor at Columbia University, told AFP.
Trump has pushed the traditional boundaries, criticizing the "so-called judge" who suspended the ban, and declaring that the decision would allow "very bad and dangerous people" into the country.
Other presidents have flexed their executive muscles, particularly when the White House has changed hands from one party to another, as it did last month.
Trump's predecessor, Barack Obama, also issued a barrage of executive orders in his first weeks in office.
Following the September 11 attacks of 2001, George W. Bush repeatedly sought to expand his powers to confront terror threats, moves criticized by opponents as infringing on constitutional liberties.
Trump, for his part, has made no secret that he intends to act forcefully to confront terror threats.
But even Bush's deputy attorney general John Yoo -- the official who drafted the so-called "torture memos" that gave the CIA latitude in using enhanced interrogation techniques including waterboarding -- warned that Trump has gone too far.
Trump has shown "little sign that he understood the constitutional roles of the three branches" of government, Yoo wrote in Monday's New York Times.
- An 'eroded' system -
Trump's actions since the ban's suspension "is fundamentally an assault on the separation of powers," said legal scholar Bruce Ackerman of Yale Law School.
Ackerman, who in 2010 predicted the advent of a "21st-century demagogue" in the White House, said the system of checks and balances has been "eroded" over several decades largely due to the polarization of American politics.
Several of Trump's campaign pledges -- his vow to repeal and replace Obamacare, reform the tax code and repair roads and bridges -- will require cooperation from Congress.
The Senate and House of Representatives can act as a powerful brake on a president, particularly if they are controlled by the opposition party.
Trump's Republicans are in charge of both chambers. But even though many lawmakers appear willing to yield to the new president, he risks resistance if he tries to ram through a radical agenda.
Some Republicans have already made clear they will not leave the new president unchecked.
After Trump was reported to be considering reviving secret prisons overseas and the use of interrogation techniques that have been widely denounced as torture, Senator John McCain and House Speaker Paul Ryan made clear that Congress would not allow such a resumption.
Many are also firmly in favor of applying fresh sanctions on Russia, despite Trump's intention to forge closer ties with the Kremlin and President Vladimir Putin.
And congressional investigations into Russia's alleged intervention in the US election continue, against Trump's wishes.
Another congressional restriction on executive power: Trump's Supreme Court nominee Neil Gorsuch faces a confirmation vote by the Senate, where Democrats are putting up a fight.
For Ackerman, the soundness of the checks-and-balance system may well be tested in the event of war or a terrorist attack on US soil, which he said could "trigger an emergency reaction that will make George Bush's (9/11 measures) seem small by comparison."