Seems silly to claim to know Sen. Manchin's motives without mentioning the politics of W. Virginia. W. Virginia voted for trump by a 35% margin and it seems unlikely that this president, or any Democrat, can overcome this deficit with rhetoric. Manchin is the ONLY state wide official in W. Virginia, which has Republican control of all other Congressional seats, both houses of its legislature (2 to one in one, 3 to 1 in the other) and a Republican governor. If Manchin's seat turns red and nothing else changes then McConnell is Senate Leader again and ALL progressive policies die. When Dems win a solid majority in the Senate they can ignore Manchin, he maintains his seat by demonstrating to ruby red W. Virginians that he has power over Democratic actions.