The Senate passed the bill by 65 votes; that's not enough for 2/3s needed to override a veto.
Because a number of the Senators were given cover by the President not signing.
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. I’m 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.