The support is coming from co-star Sam Waterston, who has played executive assistant district attorney Jack McCoy for many years on the long-running TV show.
Sources tell The Spoof that, for some time, Waterston has been eager to see Thompson (aka District Attorney Arthur Branch) get a boot in the bum, right off the show. Sam clearly coveted a promotion to the role of district attorney. When the word came down that Thompson WAS leaving, Sam jumped up and down and shouted "Yippee!" Then he accepted the promotion to the district attorney role.
Waterston, known for his liberal views, is now watching and waiting to see if the conservative Thompson will actually declare his candidacy. "Why can't that guy make up his mind? He should either pee or get off the pot," Sam has confided to friends. He's also pushing behind the scenes to get Thompson to run, get nominated, and win the election. He's nervous that if Thompson proves to be an unsuccessful candidate, he may come boomeranging back to the Law & Order set to reclaim his former job. Horrors!
Waterston's message: "Let Thompson run the country...and leave the running of the D.A.'s office on Law & Order to me."