At the end of April, after Donald Trump destroyed his rivals in the East Coast primaries, the prospect of Republican unity in supporting the nominee appeared slim.  The #NeverTrump movement appeared to have momentum, and dozens of high-profile GOP politicians were refusing to endorse Trump.

Democrats were licking their chops, believing they were looking at a contested GOP convention and a potential rejection of the Republican nominee by most of the establishment.

What a difference a few weeks make. 

The joint effort by Trump and the Republican National Committee to unite the party behind the nominee is working, and the GOP is likely to go into the Cleveland convention far more unified than anyone predicted.

Meanwhile, it's the Democrats who appear poised to blow up their convention, as Bernie Sanders supporters say they are rejecting Hillary Clinton as the nominee and are extremely unsatisfied with the direction the party platform is taking.  Sanders supporters at the convention – and they are going to be a lot of them – promise an open fight, while demonstrators outside the venue promise disruptions.

One of the reasons for the success of the GOP to unite is the instinct politicians have for political survival.  Not accepting the nominee of the party is akin to committing political suicide, and few Republicans in office wanted to take that step.  Hence the reluctant but inevitable endorsement of Donald Trump by speaker of the House Paul Ryan. 

Ryan was the highest ranking Republican to resist Trump's nomination.  But in the end, his position of opposition was untenable, and he gave in to reality.

Janesville Gazette:

The speaker of the House of Representatives says he will vote for Donald Trump.

Rep. Paul Ryan made that statement in a column submitted Thursday for publication in The Gazette, his hometown newspaper.

The statement at least partially answers a question on many minds: whether the leader of the House Republicans and chairman of the upcoming Republican National Convention would support Trump's candidacy.

Ryan has criticized Trump during the primary campaign. The two met May 12, but afterward Ryan said it was too soon for an endorsement.

A Ryan campaign spokesman said the column is an endorsement of Trump's candidacy.

Ryan wrote in the opinion piece that he and Trump have talked at length.

Ryan's column also touts the “confident America” policy agenda he has been developing since becoming speaker of the House last fall.

“Through these conversations, I feel confident he (Trump) would help us turn the ideas in this agenda into laws to help improve people's lives. That's why I'll be voting for him this fall,” Ryan wrote.

Ryan goes on to say that he and Trump do not agree on everything and that when he sees the need, Ryan will continue to speak his mind.

“But the reality is, on the issues that make up our agenda, we have more common ground than disagreement,” Ryan wrote.

Ryan also mentions the likely Democratic nominee for president, Hilary Clinton, by name, saying she is unlikely to support the GOP agenda.

“A Clinton White House would mean four more years of liberal cronyism and a government more out for itself than the people it serves. Quite simply, she represents all that our agenda aims to fix,” Ryan wrote.

Did Ryan ever have a choice?  The speaker may have believed he was acting on principle in trying to get Trump to change the tone of his campaign and get behind the House Republican agenda.  But the perception was that he was projecting doubts about the choice made by the GOP rank and file.  How could he possibly remain speaker if he rejected the choice of Republican voters?  It appears that once he realized that, he made the gradual transition to Trump supporter.

If Bernie Sanders wins the California primary next Tuesday, the idea of Democratic unity will take a huge hit, as Sanders supporters will go to the convention looking for a floor fight for the nomination itself.  Bitter feelings are already surfacing about "stolen primaries."  Hillary Clinton is not a unifying figure, and her presence at the top of the ticket will only serve to continue the party's polarization and divisions.