Maybe it's the 13000 falsehoods on the Washington Post spreadsheet that finally convinced him...
https://thehill.com/homenews/media/472378-tucker-carlson-calls-trump-full-blown-bs-artist-but-defends-him-from-media
https://thehill.com/homenews/media/472378-tucker-carlson-calls-trump-full-blown-bs-artist-but-defends-him-from-media