It may be that Ryan and McConnell told Trump that if he vetoed the bill, a few on-the-bubble votes would switch and override the veto. Im sure they told him how much of a defeat that would be.
If true, then the Republicans truly have become political enemies with the conservative base.
I only voted for P Trump
There are no more Republicans
We are betrayed
He is our last hope
And now, they expect us to give up our guns
I will make them if needed