It feels almost personal.
While he’s not come out of the gates too elegantly, Jeb came out of the gates not to subtly trying to hamstring Rubio.
Jeb came out an immediately seized the one issue Rubio was hoping would set him apart (and also mitigate, for the general election, his radical Tea Party-ism), immigration, and ran with all across the Sunday shows and dominated national coverage in a way that Rubio has failed to do (beyond reaching those Beltway pundits who are only read by other Beltway pundits).
And, he’s tied up all the big Florida fundraisers. This will hamper even Rubio’s ability to raise money for his Senate account, because he can transfer those federal dollars over to a presidential bid, so bundlers won’t want to fill that account either, but where it might really hurt is in those pseudo-outside groups (SuperPACs, 501C4s, etc), who won’t get some of those $25k-250k checks to fund his travel around the country, ostensibly doing something else, but really campaigning, and also to plain old promote his name and attack his enemies.
And all this before Jeb even gets into the game.
I still don’t think Jeb’ll get the nod. I think his time has passed. But he’ll have some of the best knife fighters in the game on his side and they’ll all be looking to take out a piece of Rubio. I suspect that, to some extent, Jeb just plain doesn’t like Rubio rising so high, so fast and stealing his thunder and that he’ll pull a Dick Gephardt (who basically sacrificed his own campaign in 2004 to take down Howard Dean) and just try to see to it that Rubio doesn’t get it (which could take the form of beating up on Rubio for President campaign or just making it too hard for Rubio, so that he stays in the Senate and misses his best/only chance to run).