Walker now joins New Jersey Gov. Chris Christie, who has been citing Bush for being “irrelevant” and “AWOL” during the big conservative struggles of the past six-and-a-half years.

The growing sense among non-Bush campaign professionals is that Bush offers Trump a convenient and powerful foil that starves the rest of the race of exposure. Walker is now joining the attack and clearly hopes to gain attention by taking on the GOP field’s top money raiser.

Walker has been toughening his rhetoric as Trump shows no sign of faltering any time soon.

In recent days Walker has called on Obama to show “some backbone” in his dealings with the Chinese, said building a wall on the border with Canada is “a legitimate issue,” and promised to defeat Islamic militants by “unleashing” the U.S. military.