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Further compounding concerns: expensive entrance fees for lawmakers, competing events like the start of the NFL season and 9/11 commemorations and some state parties struggling to drum up enthusiasm with their members.

And then there's the overarching fear " that an event once dubbed "Trumpapalooza" will indeed end up being far more about promoting the president than the candidates who are actually on the ballot.

"I've heard people say, why are we doing this? What's going on?" said Reb Wayne, a Texas-based Republican consultant. "It was a good idea at the time, but as we've gotten closer to it, I'm not sure it's going to serve much benefit."