First let's look at the constraints imposed by the structure of the federal government itself. In order for a president to be able to transform his campaign promises into reality several conditions must be met. First, both Houses of Congress must be controlled by the president's party. Second, in the Senate, the president's party must have a filibuster-proof majority, currently 60 votes. The president's party's various factions must be in agreement about his agenda. Finally, federal judges, including the Supreme Court, must be in agreement that the agenda does not run afoul of constitutional restrictions. Right now, only one of those things is true. While the Democrats have a majority in both the House and the Senate, the majority is quite slim in both chambers. The Democratic caucus is also far from united. Senators Manchin and Sinema get a lot of press, but there is a wide gulf in ideology between the liberal/progressive wing and the conservative/moderate wing. There is by no means agreement within the Democratic Party regarding the direction that should be taken. We must also take into account an opposition party that seems uninterested in anything but obstruction on the national level.
The very structure of the government written into the Constitution virtually guarantees gridlock.
The second strain of impedimenta to a president implementing his agenda is the economic structure of the country. It's not enshrined in the Constitution, but the economic system that we operate under is regulated capitalism. I say regulated capitalism rather than free market capitalism because there is without a doubt involvement on the part of the government in the way businesses can operate. Minimum wage laws, safety regulations, environmental regulations, licensing requirements and more, all impact how a business can operate. Nonetheless, government does not dictate what business you can be in, does not set prices, does not determine levels of production, nor does it effectively limit how many business you can own, despite the existence of anti-trust laws. Inflation, when it occurs, is due to a number of market forces, as well as public perception that there will be inflation. While there are things that the government, in the form of the Federal Reserve, can do to combat inflation, often times government action has unintended consequences.
Presidents usually don't have the luxury of enacting their campaign promises, but often end up dealing with unforeseen events. George W. Bush campaigned on domestic issues, relying on his executive experience as a governor of a large state, but didn't expect 9-11, which defined his presidency. Barack Obama, late in his campaign, realized that he'd be dealing with a recession, Donald Trump was riding high, bragging about a fairly healthy and recovering economy but was flummoxed by the arrival of the Covid pandemic. Joe Biden thought be could coast along as the economy recovered from Covid, but was surprised by a Russian invasion of Ukraine and rampant inflation. Nobody gets what they thought they were getting.
I'm not at all upset that an American President can't always accomplish what he wants. (Of course I am appalled at all the anti-democratic actions that are being undertaken to continue rule by the minority, but that's another story) A president who always gets what he wants with only token opposition is what's known as a dictator. We had one a few years ago who thought he was one, but we voted him out.