Former Florida Gov. Jeb Bush's (R) son, Jeb Bush Jr., has endorsed former state House Speaker Marco RubioMarco Antonio RubioCyber concerns dominate Biden-Putin summit Nikki Haley warns Republicans on China: 'If they take Taiwan, it's all over' It's past time we elect a Black woman governor MORE's (R) Senate campaign.

Rubio announced the endorsement this morning on his Twitter feed.

"Proud to announce the endorsement of Jeb Bush Jr.," Rubio wrote. "He will be a great asset in our efforts to reach the next generation of GOP leadership."

The younger Bush's endorsement of Rubio over Gov. Charlie Crist (R) will be seen as an acknowledgment that the Bush family isn't exactly on board with the governor, with whom the elder Jeb Bush has clashed.

Political realities and the establishment's decision to get behind Crist make it harder for former Gov. Bush to get behind Rubio, at least publicly. The younger Bush's endorsement gives a nod to potential donors about where the Bushes stand without being too overt about it.

Former Gov. Bush maintains a high degree of good will among conservative Republicans in the state, and his endorsement could be a game changer for Rubio. But, at this point, it appears unlikely.

The National Republican Senatorial Committee (NRSC) has endorsed Crist, whom it sees as a better general election candidate.

UPDATE: CNN reports that former presidential candidate Mike Huckabee will also back Rubio. Perhaps Bush and Huckabee will give Rubio the credibility he needs for other prospective supporters to jump on board.

Huckabee said in an e-mail to Huck PAC supporters Tuesday that their contributions would go to candidates like Rubio.

"Your contribution or $5, $10, $25 or $50 will be invested in the candidates for Senate Huck PAC endorses. Candidates such as Marco Rubio of Florida," Huckabee wrote.

-Aaron Blake