What Bush hopes to see is something that more recent entrants to the presidential race have been less and less likely to experience: a big bump in the polls.
Bush is not the first candidate to announce after seeing his national poll numbers slide; as more people talk about running, the vote is necessarily more fragmented. A Donald Trump takes some votes away from the leaders, however few. But Bush has slipped further than most, after teasing his announcement in December. His June 15 launch came just as he'd finally sunk to his pre-tease numbers.
Polling before and after campaign announcements
Real Clear Politics polling averages
Rubio's spike after his April 13 announcement is fading, again in part because of the increase in other candidates. But he already has cobbled together a tidy share of the Republican market.
We've talked before about the "lanes" of the GOP base. There are the tea partyers, who overlap with the staunch conservatives. There are the evangelicals and there are the moderates. Candidates hope to lock up a major portion of one or more of those lanes and then expand outward; Ted Cruz, for example, wants to own the conservative/tea party lane.
But no one is owning anything -- and that includes Bush, who was expected to own that moderate space.
See who else is doing well there? Marco Rubio. 538's Nate Silver wrote that Rubio sat at the happy intersection of two circles on the GOP Venn diagram: electable and ideologically acceptable. He may not be the leader of either of those, but he's doing well in both. The same holds true for his conservative and moderate credentials. He's not the most conservative; he's not the most moderate. But both groups consider him someone they can embrace.
Bush would love to be able to lock down Florida. He'd love to see a big spike in polling. He'd be very happy to secure the moderate Republican vote. In all three cases, Rubio makes it hard for him to do that.