We’ve seen the story: Trump admitted that he lied about having tapes, saying he did so in order to keep Comey honest. He also claims the plan worked.
Was this actually a smart tactic? Let's look at the law.
"Whoever knowingly...engages in misleading conduct with intent to influence, delay, or prevent the testimony of any person in an official proceeding...shall be fined under this title or imprisoned not more than 20 years, or both." 18 U.S.C. § 1512(b) (federal witness tampering statute).
However, "In a prosecution for an offense under this section, it is an affirmative defense, as to which the defendant has the burden of proof by a preponderance of the evidence, that the conduct consisted solely of lawful conduct and that the defendant’s sole intention was to encourage, induce, or cause the other person to testify truthfully."Id. at § 1512(c).
There are four mutually-exclusive possibilities, here:
1. Trump lied about having tapes to keep Comey honest. Comey was honest
2. Trump lied about having tapes to keep Comey honest. Comey was not honest.
3. Trump lied about having tapes to get Comey to be dishonest. Comey was honest.
4. Trump lied about having tapes to get Comey to be dishonest. Comey was dishonest.
Trump is trying to be clever and failing badly. He said previously that Comey lied in his testimony to Congress. Now he's saying that he put the lie about tapes out there to keep Comey honest, and that the tactic succeeded. These are inherently contradictory statements.
Regardless, Trump's raised the specter of a witness tampering charge, as the “I did it to keep him honest” tactic is an affirmative defense.