Republican presidential candidate Ted Cruz launched one of his toughest attacks yet against fellow contender Donald Trump in New Hampshire Monday night, accusing the billionaire real estate developer of being "nowhere to be found" during the debate in Congress over whether to grant amnesty to illegal immigrants.

"If you didn't stand up and fight amnesty, when the stakes were live or die, do we lose this permanently or do we win, I would suggest as voters you have reasons to doubt the credibility of the promises of a political candidate who discovers the issue after he announces for president," the Texas senator said at a town hall meeting in Whitefield.

Trump has become a figure of controversy throughout the campaign for his various immigration proposals, which have included deportation of all illegal immigrants, an end to birthright citizenship and a call to bar all Muslims from entering the United States after last month's San Bernardino terror attack.

Cruz also questioned whether Trump is a true conservative, noting donations he's made to Democrats over the years, including $50,000 in 2010 to Chicago Mayor Rahm Emanuel, the former chief of staff to President Barack Obama. And Cruz rejected Trump's self-comparison to Ronald Reagan, saying he was "pretty sure" Reagan never supported or made large donations to Democrats.

Cruz also attacked Trump for his past use of eminent domain. Trump became embroiled in controversy in the 1990’s when he attempted to use eminent domain to remove an elderly woman from her New Jersey home in order to build a new casino property.

"Donald Trump has said he thinks eminent domain is fantastic and he supports using government power to seize private people’s homes to give them to giant corporations to say hypothetically build a casino,” Cruz said. "We have an obligation to protect the rights of Americans and private property is central to the rights of Americans."

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The war of words between Cruz and Trump has intensified in recent days, with Trump going on the offensive over Cruz's eligibility to be on the ballot given his Canadian birth and for Cruz's failure to disclose loans received from Citibank and Goldman Sachs for his 2012 Senate race.

Trump on Sunday called Cruz a "nasty guy" whom no one likes. Cruz tried to turn the insult into a joke on social media Monday, posting a link to the video of Janet Jackson's hit song "Nasty."

"Donald seems to be a little rattled," Cruz told reporters before a town hall in Washington, New Hampshire. "For whatever reason he is very, very dismayed. I guess as conservatives continue to unite behind our campaign, as his poll numbers continue to go down, he's a little testier."

Trump, who was also campaigning in New Hampshire Monday, had no direct response to his rival's accusations.

Polls show Cruz and Trump locked in a tight race in Iowa, but Trump is polling considerably better in New Hampshire. Cruz embarked on a five-day swing through the Granite State this week as his numbers began to show new strength.

"The American people want a steady hand at the helm," Cruz told The Associated Press in an interview on his campaign bus Monday. "They don't want, I believe, a commander in chief who wakes up obsessed with the latest polls and driven to issue a frenzy of tweets. Instead, they want a principled, steady, conservative leader who will do everything necessary to protect this nation and keep America safe."

Fox News' Dan Gallo and the Associated Press contributed to this report.