I know that after you leave office as POTUS it is some sort of unwritten rule that you withdraw from politics.

Why did Trump not withdraw?

Also why isn’t he a senator or congressman during Biden’s term?

  • Presidents don’t generally take a demotion. Why isn’t Obama in Congress?

    Especially in Trump’s case, he’s still very much involved in politics, trying to run for another term in 2024. That’s the most impactful move he can make now, and any other long-term commitments would interfere with his campaigning (and all the legal battles he’s part of).