The Republican Party is behind Donald Trump, for the most part. Trump still struggles with some establishment GOP types, and is behind Hillary Clinton in the general election. However, the Republican Party will likely unite behind Trump, because they oppose Clinton so much. Yes, there has been a lot of noise over disgruntled party leaders upset at Trump, but rank-in-file GOP voters are behind him.
GOP support for Donald Trump is tenuous at best, but the party must support him or have no candidate in the running for the presidential election. Some Republicans, however, broke ranks recently to back Clinton, including Richard Hanna, John Stubbs and Ricardo Reyes. These political leaders cite patriotism above party loyalty, indicating that they cannot support Trump. The party overall, however, has made no indications of withdrawing support for Trump.
The GOP is not united in its support for Donald Trump. His controversial statements on immigration and racist rants have caused a rift in the party. He also did not immediately offer his endorsement to mainstream candidates such as Paul Ryan. Man in his party have gone out of their way to distance themselves and not endorse him.
I think most people in the GOP wish that Donald Trump would just go away, but it too late for that. His policy positions, when you can figure them out, are contrary to many things that Republicans stand for. He is going to hurt them downticket come November, and that isn't making them happy either.