Unfortunately enforcing any laws on congressmen is very difficult.

In all decent democracies elected politicians have immunity or similar safeguards, since the separation of powers (as theorized by Montesquieu in the middle of illuminism) which represents the foundation of democracy demands that both the legislative and executive power be separated from the judicial one.

“Making the politicians pay for their crimes” is often just a populist argument, while there are ways to incriminate them, expecting that they can be prosecuted like us normal citizens is not compatible with democracy.

You may not like what I said but I said it. Go read the original works by Montesquieu, he understood it first.

I would argue the opposite, that having members of government who CANNOT be prosecuted like normal citizens is not compatible with democracy. I would think arguments to the contrary would have to assume other impediments to a properly functioning justice system, such as politically motivated prosecutions, widespread selective enforcement, etc.

The mechanism is that voters should vote out corrupt congressmen.

This is a classic “who will guard the guards themselves?” dilemma.

Exactly. And the same is true of the judicial system btw, who must stay separate from other powers, meaning that it also has to police itself, which can create its own issues.

These are just the (little) costs of democracy. If you aren’t ready to pay them, you haven’t really considered the alternatives.

What one theorycrafter says does not make it right; nobody should be above the law in a democracy. We should have no kings in a democracy.

You said SHOULD. Yes, I absolutely agree that politicians (and I very intentionally do not call any names) should be criminally punished most harshly for abusing their position for personal enrichment or for some other egoistical goals. On the other hand, these are the people we, as totality of all voters, chose for their function. The main punishment for a politician in democracy should be the threat of losing next elections, not criminal prosecution. And of course, per definition, in every democracy every politician has a majority of citizens, who considers him stupid and in the hysterical environment of the current political life (hysterical for many more or less good reasons) such politician is not only opponent, but an enemy if not a traitor. There is an unfortunate tendency to convert this adversarial feeling into full blown hate and accusations of criminal misconduct.