Why has Jeb Bush begun arguing with Donald Trump?

Bush is rusty and making errors. He's raised money but hasn't picked up the big early endorsements expected of a front-runner. Then, Trump surged.

Jeb Bush would probably prefer to ignore Donald Trump. Why exchange taunts with an electoral distraction? Let The Donald engage with all those single-digit poll folks – the lower tiers of the big Republican presidential field. That could prevent any of them from rising to challenge Mr. Bush’s status as the establishment choice/putative serious front-runner.

But Bush is hitting back at Mr. Trump, at long last. He’s charging that the real estate mogul isn’t a conservative, and maybe isn’t really a Republican at all. Bush flew to the southern United States border on Monday to highlight his differences with Trump on immigration. Trump’s anti-immigration plans are “unrealistic," said the former Florida governor.

“He needs to be held to account for his views,” said Bush.

Why the change in tone? Long story short, Bush has little choice.

Who's the front-runner? Bush’s original nomination strategy hasn’t worked out. He wanted to be Hillary Clinton – someone who cleared the field early by showing overwhelming strength. Remember how he elbowed Mitt Romney away from running again? How he boasted early and often about the money he’d raised?

Bush’s primary target – key party figures and top elected Republicans – remained unimpressed. The establishment hasn’t really rallied behind him. He hasn’t attracted many endorsements, for instance. Look at this list compiled by the FiveThirtyEight data site – he leads the GOP field, but not by much. He’s got only a fraction of the number of endorsements Hillary Clinton has attracted.

He’s not yet a candidate of the second tier. But he can see it from where he’s standing.

Bush is rusty. Going in, everybody in politics knew Bush’s last name would present a strategic problem. Even his mom pointed out that the public might still be suffering from Bush fatigue. Trump is gleeful on this point: He’s posted an Instagram video citing the “we’ve had enough Bushes” Barbara Bush quote. Yes, she’s publicly retracted that – do you think that would stop Trump’s jibing?

What his consultants hadn’t counted on was this: Bush has been out of electoral politics for awhile. His last election was the Florida gubernatorial contest of 2002. He’s out of practice. His campaign skills are rusty. That’s part of the reason why he’s been sucked into unproductive disputes, such as the question of whether “anchor baby” is an offensive term.

While discussing that question, Bush on Monday made another error, asserting that the real “anchor baby” problem lies with Asian birth tourism. It’s true that birth tourism is a real problem that US immigration authorities want to eliminate. But why needlessly identify another fast-growing ethnicity as a problem?

“Perhaps it is still early enough in this campaign that these stumbles indicate a steep learning curve and Jeb will eventually get his footing. But if he really does want to take on Donald Trump directly, this is certainly not how that’s done,” writes Nancy LeTourneau at the Washington Monthly’s Political Animal blog.

Trump as troll. But the main reason Bush has been forced into a confrontation with Trump may be that Trump has centered much of his campaign on personal disputes. On Monday night, he renewed his Twitter attacks on Fox News anchor Megyn Kelly, for example. He’s attacked Rick Perry for his glasses, called Lindsey Graham “a total lightweight," and said Bush was “a low energy person."

He’s perhaps a troll, in the Twitter sense: someone who issues deliberately provocative messages to elicit a response.

Sometimes it’s best to ignore the troll. But if the troll is blocking your passage over the bridge, sometimes you need to address the troll. Particularly if it is leading in early polls.

Trump’s not going away. His support comes from all across the GOP political and demographic spectrum and appears solid enough to last for months. The media may be starting to take him more seriously. Perhaps the Bush campaign is, too.