Even if there indeed was no collusion, Trump could still be indicted as "accessory after the fact".
https://www.rawstory.com/2018/11/ex-federal-prosecutor-reveals-trump-can-charged-accessory-fact-putins-election-meddling/
https://www.law.cornell.edu/wex/accessory_after_the_fact
Definition
An accessory-after-the-fact is someone who assists 1) someone who has committed a crime, 2) after the person has committed the crime, 3) with knowledge that the person committed the crime, and 4) with the intent to help the person avoid arrest or punishment. An accessory after the fact may be held liable for, among other things, obstruction of justice.
Overview
Title 18 of the U.S. Code deals with crimes and criminal procedure. Accessory-after-the-fact has been codified in 18 U.S. Code § 3.
In Bollenbach v. United States, 326 U.S. 607 (1946), the Supreme Court refused to apply principal liability (either as a principal in the first degree or as a principal in the second degree) to an accessory-after-the-fact. This contrasts with the ability of an accessory before the fact to have principal liability.
Burden of Proof
According to the Federal Trial Handbook, the government has the burden of proof to show that the defendant assisted the principal offender after the crime.
Oh, what irony. Even if Trump is perfectly innocent and never colluded with Russia, he could go to jail anyways as an "accessory after the fact" because he obstructed the investigation into Putin's meddling.