Paul Ryan finally decided to endorse Trump but he's already had to distance himself from Trump's comments. It makes sense that he would endorse Trump, but endorsing Donald involves a big gamble.
On the one hand, failing to support Trump could mean losing a lot of Republican elections in November. If the Republican Speaker of the House Paul Ryan did not endorse Trump, he would have made it very difficult for the Republicans at every level of government. If Republicans don't vote for the top of the ticket, they're less likely to show up at the voting booth to vote for everyone else - from Republican congress people and governors to city council people and state senators. If party elders like Ryan turn their back on Trump, Republicans throughout the country are likely to turn their back on a slew of down ballot candidates. Those are some big stakes for 2016 who could lose the Senate - possibly even the House - along with the White House, which would give Democrats power they've had only 2 years out of the last 20.
On the other hand, voters might reasonably conclude that the Republican Party's embrace of Trump is akin to embracing his odd pronouncements. It's tough to hug a skunk and not walk away smelling badly.
If voters - particularly millennials - see support for Trump as equivalent to intolerance of women and minorities like Muslims and Mexican-Americans, that misogynist / racist label could be tattooed onto the Republican Party itself. What's at stake if the coin falls this way? Not just the 2016 race but the Republican Party's future. If they are branded as the party that distrusted scientists but trusted talk show hosts on the topic of climate change and wanted to use a religious test to determine who came into the country, and thought that our most populous neighbor should be walled off, they could easily lose the millennials who have already replaced baby boomers as the most populous group of voters.
The Republican Party could become to the 21st century what the Whigs were to the 19th century. That is, they could be the party that started strong but were obsolete before the century was over.