Republican presidential candidate Donald Trump waves to a cheering crowd during a campaign stop Tuesday, Jan. 5, 2016, in Claremont, N.H. (AP Photo/Jim Cole)
Republican presidential candidate Donald Trump shows off recent poll numbers during a campaign stop Tuesday, Jan. 5, 2016, in Claremont, N.H. (AP Photo/Jim Cole)
Republican presidential candidate Donald Trump said he was advertising on TV, spending at least $2 million per week, to play it safe. Still, he insisted he was confident about his position in the race and his huge level of support. (Associated Press)
Republican presidential front-runner Donald Trump released his first television ad of the campaign Monday, using footage from Morocco to promote the wall he plans to build "on our southern border" with Mexico.
Republican presidential front-runner Donald Trump released his first television ad of the campaign Monday, using footage from Morocco to promote the wall he plans to build "on our southern border" with Mexico.
Donald Trump is fighting to keep his place at the top of the polls in New Hampshire. This week, he laid into New Jersey Gov. Chris Christie for embracing President Obama in 2012 in the aftermath of Superstorm Sandy. (Associated Press)
Republican presidential candidate, businessman Donald Trump addresses supporters at a campaign rally, Monday, Dec. 21, 2015, in Grand Rapids, Mich. (AP Photo/Carlos Osorio)
Republican presidential candidate Donald Trump addresses supporters at a campaign rally, Monday, Dec. 21, 2015, in Grand Rapids, Mich. (AP Photo/Carlos Osorio)
Republican presidential candidate Donald Trump poses with supporters after a campaign rally, Monday, Dec. 21, 2015, in Grand Rapids, Mich. (AP Photo/Carlos Osorio)
Republican presidential candidate, businessman Donald Trump addresses supporters at a campaign rally, Monday, Dec. 21, 2015, in Grand Rapids, Mich. (AP Photo/Carlos Osorio)
Republican presidential candidate, businessman Donald Trump addresses supporters at a campaign rally, Monday, Dec. 21, 2015, in Grand Rapids, Mich. (AP Photo/Carlos Osorio)
Republican presidential candidate, businessman Donald Trump addresses supporters at a campaign rally, Monday, Dec. 21, 2015, in Grand Rapids, Mich. (AP Photo/Carlos Osorio)
Donald Trump has been a target for Democrats' attacks throughout the campaign. But the attacks have grown sharper as he defied predictions that his unconventional campaign would flare out and remained atop most polls. (Associated Press)
Immigration issues have been the lifeblood of Donald Trump's campaign, including his pledges to build a wall across the southern border, deport illegal immigrants and temporarily bar Muslim visitors from entering the country.
Democratic presidential candidate Hillary Clinton speaks about recent comments from Republican presidential candidate Donald Trump during a campaign stop Tuesday, Dec. 8, 2015, in Salem, N.H. (AP Photo/Jim Cole)
Democratic presidential candidate Hillary Clinton speaks about recent comments from Republican presidential candidate Donald Trump during a campaign stop Tuesday, Dec. 8, 2015, in Salem, N.H. (AP Photo/Jim Cole) ** FILE **