Republican presidential front-runner Donald Trump dismissed establishment favorite Jeb Bush as unelectable and "low-energy" Wednesday, while the former governor labeled his rival a tax-hiking Democrat in a war of words played out at dueling town halls. 

In Derry, Trump drew a capacity crowd to a high school auditorium of almost 1,000, and filled a few overflow rooms. He started his criticism of Bush in a briefing with reporters and continued in the town hall. 

"I don't see how he's electable," Trump told reporters, later describing Bush as a "low-energy person" who has trouble getting things done. 

"Right down the road, we have Jeb," Trump said early in the town hall, drawing boos. Trump mocked Bush for going "down like a rock" in early polls in the state and failing to excite his supporters. 

"You know what's happening to Jeb's crowd?" he asked. "They're sleeping." 

In nearby Merrimack, Bush, who had once been reluctant to go after his opponents, portrayed the billionaire businessman as a tax hike-promoting Democrat whom voters would eventually tire of. 

"I think what people are eventually going to vote for is a proven conservative leader that's done it," Bush said in a video of the event released by his campaign. 

He went on to criticize Trump for his past contributions to Democrats, as well as his changing positions on tax issues and his previous support for a single-payer health care system. 

"He's won over a lot of people. People are very angry about how Washington's not working. He's tapped into that," said Bush. "But when people look at his record, it is not a conservative record." 

Trump, who has moved to the top of summer polls, and Bush, who remains the favorite of establishment donors, have been clashing frequently in recent weeks over a number of issues -- especially immigration. 

Bush's wife was born in Mexico, and he has said that people entering the country illegally do so as an "act of love" for their families. 

Trump, who is calling for the mass deportation of people who have entered the country illegally and the building of a giant wall on the border, mocked such rhetoric. Trump also defended the use of the term "anchor babies" and bragged about the wall he plans to build along the Mexican border, saying it would look good as well as keep people out. 

Bush on Wednesday criticized Trump's immigration platform, arguing that it's "not a conservative plan" because it would cost tens of billions of dollars to carry out. 

Trump told reporters before the town hall meeting that his plan would likely pay for itself in a year because of all the money the government would save. 

Trump, who has been criticized for a lack of specific policy plans, skipped an all-day education forum attended by half a dozen of his competitors, including Bush.