TLDR: Congress is more powerful. Obama was being constantly shut down by Congress. A lot of things Trump has done would not be acceptable under Obama's belt. Those white yippies would have had him out the office. It'S REALLY HARD BEING A YE FAN RN, I JUST WANT MY FUCKING MUSIC *****
WHERES THE ALBUM, FUCK ALL THIS BULLSHIT.
If the Congress were unified and voted together, they can pass any law they please. The President can't pass any laws himself and couldn't stop a law Congress was determined to pass, only delay it momentarily with a veto they could override.
Most of what the government does is determined by law. Laws determine how much money the government raises, from what sources, and for what purposes. 99% of government jobs exist because Congress created them. Every building, every program, every cabinet position, every everything, save a very small number of things explicitly mentioned in the Constitution, which only requires a few things - so the Postal Service but not the State Department or Justice Department, the Supreme Court but not the District or Circuit Courts, the President and Vice President but not the Treasury Secretary or UN Ambassador.
Congress could make the Supreme Court three justices, or thirty. They could get rid of the FBI, NSA, and CIA, or double their size. The president couldn't do any of that, and s/he would not be able to stop them if they were unified.
If they're unified, they can even remove the president from office. He can't do that to them on his own.
It gets a little mirkier in certain areas, such as war. Only the Congress can declare war, but the President is Commander-in-Chief so in practice it's tricky. So that's one caveat to them being clearly more powerful. But, the Congress could cut all funding to the military and then who would the president command?
There are also many government actions taken by a President's Executive Order or by regulations written by people who work for the president. That is true. But an act of Congress trumps those things in most cases.
The biggest caveat of course is that Congress is rarely unified. If it speaks with one voice, it is the most powerful branch of government, without question. However, how often does Congress speak with one voice? In practice, almost never. Even then, if there's anything close to unity, it's probably in agreement with the president. One time the Congress was close to unified in opposition to a president was against Andrew Johnson, Lincoln's successor. Congress did whatever they wanted irrespective of his wishes, overrode most of his vetoes, and even impeached him. Had they been fully unified they would've done even more.
All of this is oversimplified and there's plenty of room for debate when you get into the details, but the overriding truth is this: The Congress is potentially much more powerful than the President in many respects, but their power is fragmented. The President is not as powerful as the Congress in many respects, but his/her power is concentrated. It creates a unique balance of power that ensures no one person or institution ever becomes too powerful for too long, while still enabling a strong central government to react to the needs of the day without getting too far from the will of the people. This is the genius of the U.S. Constitution.
I have to agree with James Yune Parkson that The Supreme Court is arguably more powerful than either Congress or the office of President. But it's actually more nuanced than that. See the Supreme court can't just make a decision out of the blue, before they can make a determination, it has to appear on their docket. (in other words someone outside of the court has to challenge the law, and it has to make it through a rather complicated process to appear before the Supreme Court)
Now Congress, is the only branch of the Federal Government able to write or pass 'Laws', The President can't, he can propose them, he can sign them, he can veto them, but he can't write them and he can't pass them against legislative opposition. Congress on the other hand can pass a law the President has Vetoed. Congress can also, given sufficient support amend the very Constitution, though the Amendment has no force until passed by a majority of states, something else the President is powerless to change.
Possibly the most powerful tool the President has, arguably more powerful even than Executive Orders (which can only apply to existing law) is Presidential Pardons. Which isn't to say the office has no teeth, it does. It simply has to wield it's tools carefully, with subtlety and diplomacy