Your analysis is right and accurate. I agree completely.
I am sorry to say that all It takes for the base, is not so much the sense of betrayal they feel, but the appearance of weakness in a man they elected to be a fighter.
Trump had a choice, the veto. He could call the Congress back into session to pass one more Continuing Resolution. He then could do his best to renegotiate a replacement bill with the House GOP to fund the wall (huge symbol to the base) and defund Planned Parenthood.
Ultimately this would go to either a 51% reconciliation vote in the Senate or force a House/Senate Reciliation Committee. Let the Democrats dare to try to defund Defense with the mid-term elections 6 months away.
I am not prophet enough to know if this scenario would prevail, but this is the kind fight in Trump we expected and voted for. The President said he will not vote for such a bill again. This is insufficient. This bill precludes another funding bill for two years.
To retrieve his base the President must ACT soon in some way with the honesty, strength and intrepid courage his base thought they voted for in 2016. I want to vote for that man again. We need reassurance in action, and we need it now.
Susan Collins and Lisa Murkowski support PP funding. There are not the votes to defund.
If the Republican leadership in Congress was principled, it could exclude PP funding and let the Dems and Collins and Murkowski try to shut the government down until it is funded.
But, once the funding is the legislation, Trump gets the blame for any shutdown if he vetoes it.
Which every party gets the blame for a shutdown takes a beating the polls.