It’s not a shock that Thompson can’t announce his presidential candidacy until June because of his commitments to “Law and Order” and “Paul Harvey.” I figured that was the problem. From Novak’s column:

Although revelation of his cancer history has cleared the decks for Fred Thompson to run for the Republican presidential nomination, his commitments as a television and radio performer may delay his announcement until June.
As an actor on NBC’s “Law and Order,” Thompson can scarcely abandon the show during the May ratings sweeps and has taped programs that will be aired then. He also has commitments to ABC as a stand-in for radio commentator Paul Harvey.
There was no reason for Thompson to make the cancer revelation if he did not plan to run for president, and this indicates he intends to join the race. However, prominent Republicans are delaying an endorsement until he actually announces his candidacy.

Well, that’s a good idea, why endorse a candidate until he’s announced, especially when it doesn’t look like Thompson needs any more encouragement to enter the race.
(via)