Although Jerome Powell is the Fed chairman but he does not have sole authority to make decisions on interest rates. Like any agency in the US, lowering or raising interest rates requires a vote and according to the news, there were 9 votes in favor of maintaining interest rates and only 2 votes in favor of lowering interest rates.
If it is as simple as you stated, Trump would not dare attack any FED Chairman, but he knows that if he wants it done, it would be done. Fine, it's all about the decision and the votes of the Board of Governors of the Federal Reserve (Board) and the Federal Open Market Committee (FOMC), yet the position of the FED Chairman is powerful and influencing. He has the power to convince his colleagues to vote for a rate cut. Who knows if he is the one influencing the rate hold just to annoy Trump more?
FOMC consists of 12 members, including 7 governors and 4 presidents of the 11 presidents of the 11 Federal Reserve banks of the US. Powell is the 12th member and like the other members, he has only one vote. Of course, he can use his power and influence to convince other members, but if they refuse, there is nothing he can do.
Like Trump's presidency, he has power, influence and the ability to persuade members of the Democratic Party. But the final decision is still theirs, what can Trump do to the Democrats if they vote against his bill?
Not to mention, the Fed's mission is to maintain the strength of the USD, ensuring the US and world economies are always in the best condition without being politicized.
Politics is much more complex and beyond our understanding. So I just discuss based on theory and constitution, I don't like to speculate, make assumptions because if discussed that way, anything can happen.