The Bush-Rubio game of survival: It’s been bubbling behind the scenes for weeks, and yesterday the fight between Jeb Bush and Marco Rubio broke out into the open. It’s getting very prickly between the two Floridians, and here’s the big reason why: Both have reason to be disappointed in their fundraising this past quarter, and they both need a boost fast. Bush’s $13.4 million haul didn’t impress a lot of observers, but he can claim that his total beat out Rubio’s $5.7 million (and Ted Cruz’s notable $12.2 million, by the way). Team Rubio was quick to boast that their $11 million cash on hand number is more than Bush’s $10.3 million – complete with a press release implicitly dinging Bush for being careless with donors’ money. And then came a counterargument from Rubio foes, who pointed out that a chunk of the Florida senator’s cash is earmarked for the general election, making his actual primary race cash-in-the-bank figure less than Bush’s. And that’s not to mention Bush’s suggestion that he’d legislate against the “dark money” Rubio’s largely relying upon. You’ve even got Jeb Bush Jr. stating publicly yesterday that Rubio should “drop out or do something” because he’s not doing the job he’s been paid to do. Oof. It’s getting ugly.

Why so aggressive? The reason for the feuding between Rubio and Bush comes down to this: They’re both competing for the same donors, and both are feeling pressure to show progress. And frankly, they’re both stuck in the second tier right now. Bush is trying to jump-start a surge with a massive TV buy, hoping that by November, polls will consistently show Bush at the top instead of treading water. For their part, Rubio’s camp has been trying to will momentum into appearing, but the facts haven’t yet matched his perceived potential. He too needs to show progress soon if he wants donors to start viewing him as the best establishment investment.