By Matthew Price
BBC News, New York
This was a big night for John McCain.
His victory presents a difficult choice for the Republican Party. More of that in a bit.
First though, let's look at the 71-year-old senator from Arizona. He was beaming from ear to ear when he made his speech after winning a broad swathe of states across the country.
"Tonight, I think we must get used to the idea, that we are the Republican Party front-runner," he told a cheering crowd.
He won the glittering prize of winner-takes-all New York, and he did not stop there.
He also took the other big prize, California, and a host of other states lying in-between these two coastal territories.
What many do believe, is that Mr Huckabee, for whatever reason, has decided not to drop out of the race in order to help Mr McCain seal up the nomination
Importantly, he also took Connecticut and Delaware: names that might mean little outside this country, but which mean a lot to a politician running for the White House.
They are both winner-takes-all states.
So while he is not unstoppable, as he tots up the all important delegate numbers from Tuesday's victories, Senator McCain will see that he is now ahead by quite a margin.
If the former Vietnam vet had a good night, his arch-rival Mitt Romney, certainly had a bad one.
Mitt Romney failed to spring any surprises
Not because he did not win anything. He took some useful states, like the state he once governed, Massachusetts.
However, he did not have any surprise wins. And to rub it in, the other Republican nominee still in the frame, Mike Huckabee, did.
The Baptist preacher swept the south. He won Georgia, West Virginia, Tennessee, Alabama and of course Arkansas where he was once governor.
Mr Huckabee is not only winning headlines from Mr Romney. Both men get a large amount of their support from the more conservative elements of their party, and Mr Huckabee is also taking votes off his opponent as well.
And that is helping John McCain.
Indeed there is a growing suspicion that Mike Huckabee is staying in the race to do precisely that. He still says he can win, but many pundits just do not believe that.
What many do believe, is that Mr Huckabee, for whatever reason, has decided not to drop out of the race in order to help Mr McCain seal up the nomination.
Mr McCain and Mr Huckabee may not agree on all aspects of policy, but they do both share a mutual dislike of Mr Romney.
So what of the importance of the night for the Republican Party?
Well, there are some "ifs" coming up, but if Mr McCain does go on to get half of the delegates up for grabs, and goes on to win the Republican nomination, will the Republican Party coalesce behind him, or will the party tear itself apart?
The idea of a Republican civil war may sound far-fetched, but Republicans are by no means united behind their new front-runner.
One big problem is that in general terms they are pretty unhappy, not just with the way their party and country has been run under George W Bush (and opinions differ as to how to rescue the party).
They are also, again generally speaking, unhappy with the candidates running for the nomination.
A number of prominent Social Conservatives - the most influential group within the party - are actively campaigning against Mr McCain.
One conservative pundit even went as far to say that she would rather vote for Hillary Clinton than John McCain. Point made.
Many social conservatives see Mr McCain as too bi-partisan, too willing to work with the Democrats, too liberal on issues like immigration.
Would a McCain nomination turn the Republicans against themselves? It is the fear many in the party will have if Mr McCain manages to maintain his front-runner status, and get the nomination.