From Jonathan Bernstein:
Trump hasn’t demonstrated firm positions on specific items in the budget talks, nor has he proved effective at pushing through any particular initiative. In his public statements, he’s given very little evidence that he understands the issues involved, whether it’s Deferred Action for Childhood Arrivals or suspended Obamacare payments to insurers or the policy questions surrounding raising budget caps. On all those issues, he’s come down on both sides in recent months. Does he even understand the congressional context and rules involved in reaching an agreement? There’s no evidence of that. And he’s broken commitments to leadership (on both sides of the aisle) before.
So the smartest thing for all concerned is to just treat the president as if he would automatically sign on to any deal that was reached while ignoring any specific input he may have up to that point.