TV ads are for LIVs: people who can be persuaded in 30 seconds.
By definition, you want to pummel them, 30 seconds at a time, no earlier than 3 weeks out. Otherwise, you are beyond their attention span.
The campaign MO of a candidate leading by far in funding is to let all the other candidates freak out about exposure and positioning in the lead up while you stay above the fray.
And then... Blow them all out of the water 6 weeks out. (3 weeks before early voting starts through Election Day).
El Jefe spending money now means HE is one of those candidates freaking out about exposure and positioning in the lead up.
It means he’s seriously off his game plan to be the reserved money leader who can act decisively when it counts.
The second reason a well funded candidate would take to the TV airways early is as a preemptive strike against less well funded opponents. To use a boxing analogy, by buying a large block of television advertising early Bush is looking to knockout at least some of his opponents.
Of course Trump's entry into the race is a wild card and his harsh rhetoric aimed at Bush may be a third reason to start running television ads sooner than later. This would again comport with a sound political principle of not letting your opponents define (or redefine) you first.