The world has fundamentally changed since Trump’s last rally. His greatest hits may not land the same way anymore. And the campaign has struggled to find a clear message. Here’s what I know: Trump often uses rallies to send out trial balloons when shifting or honing his pitch.

Today’s crowd may be smaller than expected, but this is his true base, and their reactions to what he says tonight (and how he says it) will likely have a big effect on the president’s messaging going forward.

The president needs a clear cultural target to rile up his base; that’s been his strategy in the past. Think: the wall! Will he find an opening tonight? I’m on the lookout for what he says about immigration, confederate statues, the NFL, and masks.

This is all to say the crowds and rallies are not just about ego. They have been a crucial sounding board in the past. Trump's talent for finding what has base feels is uncanny; in turn, he also has a profound influence on what his voters think — once he lands on a fixed position

The Trump campaign rally dialectic has its own logic, hard to understand for those who haven't attended. But these events are a fountain of energy & ideas & pure id. Dark rhetorical turns in the past have often followed positive reactions to off-the-cuff remarks at these rallies.