Republican presidential candidate Jeb Bush slammed rival Donald Trump, calling him a jerk during at a town hall meeting in New Hampshire. (Reuters)

For nearly a month, Jeb Bush has established himself as the leading Donald Trump attacker, convinced that relentlessly criticizing the Republican front-
runner’s temperament and rhetoric will draw fresh support.

So far, it hasn’t worked very well.

Bush remains stranded at the back of the GOP pack, polling at around 4 percent nationally and little better in the early states of Iowa and New Hampshire. Trump, meanwhile, has actually gained ground over that time — and has only intensified the barrage of insults he routinely lobs at Bush.

In the past week, Bush has called Trump a “jerk” who is “not serious” and is running a “chaos campaign.” The former Florida governor has also run ads calling Trump “unhinged” and also torn into the front-runner for praising the leadership qualities of Russian President Vladi­mir Putin and for talking about deporting Latinos and barring Muslims.

Republican candidate Jeb Bush throws a fist in the air after hugging political activist Beverly Bruce at a town hall style meeting at Nashua Community College in Nashua, N.H., on Thursday. (Melina Mara/The Washington Post)

“I’ll continue to call Trump out for his outrageous comments & naive ‘foreign policy.’ Even if no one else will,” Bush tweeted Monday.

Trump, of course, has responded in force, hitting Bush almost daily with a mix of his trademark insults and put-downs on social media, at rallies, in television interviews and on the debate stage. Amid his regular barbs at Bush as too “low energy” to be president, Trump in recent days has called him “a weak and ineffective person” who is “going to be off the stage soon.”

“Being at 2% and falling seems to have totally affected his confidence,” Trump said of Bush on Twitter. “A basket case!”

Bush’s decision to go after Trump comes with risks, as Sen. Lindsey O. Graham (R-S.C.) learned this week. The senator ended his White House bid Monday after facing strong attacks from Trump, who once gave out Graham’s cellphone number to a large crowd in retribution for an attack. Gov. Scott Walker of Wisconsin, Gov. Bobby Jindal of Louisiana and former governor Rick Perry of Texas also tried concerted attacks on Trump before dropping out of the Republican race.

Bush, who long vowed to run “joyfully” above the fray, is clearly uncomfortable as an attack dog and often appears hesitant or awkward in the role. He stops short of refusing to support Trump if he wins the party’s nomination, and Bush demurred when asked on CNN if Trump would be a better president than Democratic front-runner Hillary Clinton.

On NBC’s “Meet the Press” on Sunday, Trump said Bush is “an embarrassment to the Bush family, and in fact he doesn’t even want to use the Bush name, which is interesting.”

Bush said on CBS’s “Face the Nation” that “I don’t take it personally” when Trump hurls insults. “He shouldn’t take it personally either, but someone needs to call him out,” Bush said.

New Hampshire voters listen to Republican candidate Jeb Bush at a town hall style meeting at Nashua Community College in Nashua, N.H., on Thursday. (Melina Mara/The Washington Post)

Bush trails far behind Trump and Sens. Marco Rubio of Florida and Ted Cruz of Texas. Trump received 26 percent support among likely Republican voters in New Hampshire in a poll released Friday by Franklin Pierce University and the Boston Herald, while Bush was in fourth place at 10 percent in his strongest state. That same day, a Fox News survey of Republicans nationally showed Trump getting 39 percent and Bush 3 percent — record highs and lows, respectively, for the two.

The idea that Bush is the only candidate brave enough to take on Trump is a theme strongly embraced by his campaign and supporters in recent days. The campaign has released several slickly produced anti-Trump videos — including one released Monday that faults Rubio, Cruz and New Jersey Gov. Chris Christie for failing to confront Trump. When Trump accused Bush on Twitter of distorting his statements, the Bush campaign replied later with a web-only video to bolster his points.

Separately, Right to Rise USA, the super PAC backing Bush’s bid, is airing a new ad nationally on Fox News Channel that uses debate clips to highlight Bush’s attacks on Trump. Another message airing on Fox labels Bush “One candidate tough enough to take on the bully. . . . One candidate tough enough to take on ISIS.”

The super PAC had vowed to focus on positive advertising, but its ads are now roughly two-thirds negative and one-third biographical, according to a person familiar with its plans who requested anonymity to speak frankly about the group’s strategy.

The PAC’s spending plan remains critical because it raised $103 million even before Bush declared his candidacy, giving him a sizable cash advantage over his rivals. A recent Washington Post analysis found that the group has spent nearly half that much so far.

Many donors say they are pleased with their candidate’s focus on the front-runner.

“It’s important to stand up against Donald Trump. It’s a risky strategy, but he does not represent the values of the vast majority of the party and, frankly, I wish the [Republican National Committee] didn’t feel like it needs to be so neutral,” said William Kunkler, a Chicago-based businessman and Bush bundler. “I think we’ve got to write rules that if someone behaves this way, you disqualify yourself.”

Another Bush bundler, who requested anonymity to discuss campaign strategy, said that “conventional wisdom for a long time was don’t bash Trump because it would hurt you. Well, Trump has thumped Bush enough, the poor bastard, that by hitting back it might just move his numbers up. This may be less about bringing down Trump’s numbers but instead to bring Jeb’s numbers up because he’s standing up to the guy. And nobody else is trying this. He’s showing that he’s not a low-energy, let-the-bully-get-away-with-it kind of guy.”

After the holidays, Bush will spend most of his time campaigning in New Hampshire, the state considered most critical to his chances, although he also plans two campaign stops in Iowa in January, according to a campaign aide. Bush also will make at least one visit to South Carolina around the time of a Jan. 14 presidential debate there.

After a fall spent criss-crossing the country to campaign, raise money and appear in televised debates, early-state supporters want Bush to settle down and focus primarily on meeting voters.

“This campaign is built to go the distance, which means apportioning time among all the early states and those that follow, vs. candidates that are putting all the chips on the table to eke out a finish in one state and leverage that and leapfrog to the next one,” said David Oman, an Iowa Republican operative. “You could argue there’s no right or wrong in that, every candidate and campaign gets to choose their strategy. Some are different this cycle.”

Said New Hampshire state Sen. Carlos Gonzalez, a Bush supporter: “We’ve closed out the debate stage of the campaign. Now you have to position yourself to reach out to the people. The more exchanges with people, the better the governor’s message will be received.”