Mitt Romney's primary trifecta in Wisconsin, Maryland and the District of Columbia means the end of the primary season.
It is not just that Mitt Romney won as expected, but how he won.
If Rick Santorum was to mount a realistic challenge, he had to have polled better beyond conservative evangelicals. They were his base of support and were responsible for his victories in the deep South. This has not happened, the reverse has been the case, with Romney starting to do better with groups with whom he had formerly had problems.
The exit polls are once again showing increased concern among Republican voters about the fratricide taking place in their own party and they are coming around to the position of the Republican leadership - that is time to stop the contest, even if Rick Santorum argues that half of the country has not yet been heard from.
Romney, in his victory speech, effectively outlined the economic differences between himself and Barack Obama, and is back in campaign rather than primary mode. He is concentrating on November 6 rather than on the primaries in April and May.
The party professionals and the pundits are treating Rick Santorum as if he was a contestant on a television game show, where the contestant, if he perseveres, accumulates appreciably higher winnings, but if he flubs the question he risks losing all that he has accumulated.
Santorum is being congratulated on coming from nowhere and succeeding on a shoestring in giving the Mitt Romney campaign a scare. Santorum has reestablished himself as a bona fide political leader.
Given the Republican tendency to pick second-place finishers in the previous election cycle's primary season, Santorum would be the beneficiary of that tendency - in case Romney loses to Barack Obama. Fold, pocket your winnings, and leave the table graciously they are telling him.
The compliments and the promise of better things to come are also accompanied with a pointed warning: If you do not fold graciously, you risk throwing away all that you have accomplished. This is particularly the case with regards to the Pennsylvania primary scheduled for April 24. Santorum has identified it as his firewall, till May brings him back to the favorable terrain of more conservative states.
Pennsylvania is Rick Santorum's home state and in the latest poll he is leading Mitt Romney by 6%. This margin is much smaller than the 20% bulge Santorum had 2 weeks ago. If Santorum decides to stick it out, the Romney ad blitz could achieve in Pennsylvania what it achieved in other states - namely, wiping out the Santorum lead and giving the win to Romney.
Losing Pennsylvania for Santorum will not be like losing neighboring Ohio. Santorum will be saddled with an albatross as a candidate who could not even carry his home state. If he does win, it will not be considered a pivotal victory and the margin of victory will be scrutinized compared with Romney's lopsided victory in his home state of Massachusetts.
It will take a tremendous amount of either courage - or foolhardiness - for Santorum to stick it out.