Mueller's report is a call to action for Congress
Quotes from the report (pasted from a diary on Daily Kos):
But Mueller also concluded that Congress's proper function in this situation was to exercise its powers under our constitutional system of checks and balances to make sure that no person is above the law. "We concluded that Congress has authority to prohibit a President's corrupt use of his authority in order to protect the integrity of the administration of justice," Mueller wrote.
Mueller also explained why this is constitutionally proper. Congress can permissibly criminalize certain obstructive conduct by the President, such as suborning perjury, intimidating witnesses, or fabricating evidence, because those prohibitions raise no separation-of-powers questions."
Congress must act, must impeach. Starting with Meullers Testimony to Congress, and all the other investigations, and moving relentlessly and rapidly (no waiting for court delays- any obstruction via the courts would just be added to the articles of impeachment) to formal impeachment hearings, by fall at the latest, before the primaries.