If the President were to lean on them, say by calling for permanent tax cuts, loudly and often, that would make a tremendous difference. If, as you say, he's gotten his way every time he's demanded tax cuts, then he has no reason not to push for it now. It's such a ridiculously simple task for him, in stark contrast to his wild ideas for "reforming" everything in sight. The fact that he declines to take such a simple step raises serious questions as to how much of an ally he really is.
Not worthy of comment.
If, as you say, he's gotten his way every time he's demanded tax cuts
He has. Look it up.
If the President were to lean on them, say by calling for permanent tax cuts, loudly and often, that would make a tremendous difference
Done. Time and again. Where were you?
Contrary to opinion, the President doesn't rule the Senate. Liberal Republicans stood in opposition of making them permanent. The President's pressure, fancy footwork by the House in the bill, and Americans burning up their phone lines made the Libs cave to temp cuts. Supposedly we now have a (barely) conservative majority in the Senate, whereas before it was only a Republican majority. We'll see how that affects the ability to make these cuts permanent.
I find it a waste of time to pressure the President on policy he is aligned with us on. In this instance, working WITH the President against Liberal obstruction in the Senate will yield greater reward. I save pressure against the Prez on issues I do not find him to be in agreement with, such as immigration.