While it isn’t apparent from looking at recent events, senators are actually some of the most powerful people in US politics. That’s because they are the smaller chamber of the US legislative branch.

Why I say they are powerful is that they (along with the house) dictate laws and the budget for the US. While the house, the larger chamber of the legislative, performs a similar role the house has 435 people vs the senate’s 100 (meaning the power of the senate is less diluted).

While looking at the current affairs in the US might seem to imply Trump is all powerful. Right now he is only able to do what he is doing becuase Republicans effectively control all three branches of the US federal government (legislative - makes laws, executive - executes laws, judicial - evaluates/interprets laws).

If they wanted to, the senate could stop a lot of what Trump is doing. If they had support of the house, they could literally kick him out of office. While the judiciary also has a lot of power, it’s more reactive rather than proactive when compared to the legislative.

So In summary a senator is one of the top law makers (as in literally defines the law) in the US. And if senate and house work together, they are the most powerful branch of the US government. The main issue is getting 635 people to agree on anything, which is why over the past couple decades the executive had been able to exert power power/influence in the US.