We don't have to assume that Biden is weak. Why not? Let's assume for a moment, that he is super-intelligent, and a super actor. Let's say that he is feigning borderline mental incapacitation. Why? People don't fake getting old. They don't fake losing their integrity. The only reason why Biden might be faking like he is borderline insane is, if he loses the presidency, and the Trump people win, he can plead insanity in court for the many things he is ordering against the Constitution. And there is a lot of evidence to back this insanity idea up, if you compare what Biden has done with what the Constitution says.
The simple reason why the Dems are using Biden is, he can be completely manipulated. For example, nobody could manipulate Trump as directly as they are manipulating Biden. Trump seldom used a prompter. But Biden is losing it badly enough that he is failing in his use of a prompter.
In addition, the odds in past president elections are that the incumbent was the best chance a party had to get their man in. And they want Biden in, because he can be manipulated so easily. So, outside of him really losing it completely, they will go with him.
Joe Biden So Weak He Reads Softly from Note Cards During His Meeting with Israeli Leader - https://www.naturalnews.com/2023-10-19-pfizer-cuts-costs-decline-covid-medication-uptake.html
Funny you mention Biden can be manipulated while Trump cannot. It is a little bit off topic, but it is obvious Republicans within the establishment tried to manipulated Trump onto being with their establishment, instead Trump managed to break loose and do whatever he wanted to as a president.
So yes. I believe both parties are capable of trying to influence over their president to push forward specific policies, though. I still do not think Biden is a puppet. He could be indeed being influenced by his party, but that is different than being a political puppet who obeys people behind the curtain.
If Trump managed to get back into the White House, he would be certainly unleashed and even the Republican party could not influence over whatever policy he has in mind.
Since Trump is for the people, absolutely let him unleash whatever he can... even against his own party leaders, many of whom are almost as corrupt as senile Biden.