I'll take a stab at that one, the system is functioning exactly as it should.
Congress is clearly searching for something to hang Trump with, and they think they will find that something in his tax returns. They aren't seeking information to aid them in creating law, they're fishing. The courts will determine if that action falls within their purview. That's how the system works, how it was designed to work.
Why do you keep repeating these false statements? Congress is not fishing, they have large piles of evidence that indicate Trump has repeatedly engaged in criminal activity involving his finances. Like, very large piles. They would be derelict in their duties if they didn't investigate him. Surely you can at least admit that Congress has lots and lots of evidence of financial misconduct, no?
Furthermore, the legal argument you're advancing now has been adjudicated by the courts twice and they found the argument so lacking in merit that they said Trump's lawyers failed to even advance a 'substantial legal argument', which is basically one step up from having the court fine them for wasting everyone's time with frivolous lawsuits.
The anti trump folks want congress to take out Trump and don't mind if they're overstepping their bounds to do it, but they forget that someday the republicans will control congress again and posses that same power.
You can't possibly be serious here as this is some bizarro-world logic. Congress has ALWAYS had this authority and Republicans have used it for vastly less important things than this as recently as two and a half years ago. Where are you getting this nonsense?
The actual problem here is that the executive is advancing radical, authoritarian legal theories that usurp the power of the legislative branch so that they can cover up Trump's criminal activity. Under Trump's theory Congress can impeach the president for being bribed but is prohibited from finding out if he's actually being bribed first. Clearly that's a nonsensical theory meant to protect a criminal executive branch and it's an egregious violation of our Constitution and the rule of law. You want a dictator? Saying he can't be investigated for crimes is how you get a dictator.
You may want to take your own advice and remember that someday Democrats will control the presidency. Do you want the next Democratic president to be able to commit crimes with impunity?