Both the Bush and the Rubio campaigns are motivated by an unshakeable conviction that Trump will eventually decline. That conviction is shared by most political insiders. Perhaps it is correct, although each day forces those insiders to adjust their estimate of how long Trump can stay aloft.

In the meantime, the would-be frontrunners, Jeb and Marco, are reduced to bragging about flying commercial and taking UberX. The donors will apparently be pleased.

But it won’t solve Bush’s and Rubio’s problem. At the moment, Trump is leading because he seems big and they seem small. More voters believe Trump will be a stronger leader than either Bush or Rubio. Trump’s put-downs of both men — that Bush is “low energy” and that Rubio is a “little boy” — are outrageous but effective ways of reinforcing voter concerns that Bush doesn’t have the drive to be president and Rubio doesn’t have the maturity.

There’s still time for those perceptions to change. But for the moment, Bush and Rubio are fighting over who has the resources to stay alive until Trump begins to fade — if that ever happens.