At least five new ads were unveiled or started airing Monday. Here's a look at them:
Republican front-runner Donald Trump is pumping cash into a television ad buy for the first time -- ordering $2 million this week in broadcast, cable and radio time in Iowa and New Hampshire, according to Kantar Media/CMAG.
His 30-second spot focuses on two of his most controversial proposals: Building a wall along the U.S.-Mexico border and banning Muslims from entering the United States.
Bush goes after ISIS, too
Former Florida Gov. Jeb Bush's campaign plays up the threat of ISIS in a new ad airing in New Hampshire.
"The United States should not delay in leading a global coalition to take out ISIS with overwhelming force," Bush says in the spot, which uses audio from his foreign policy speech at The Citadel in South Carolina. "We are at war with radical Islamic terrorism. We have but one choice: to defeat it."
Cruz mocks Rubio's fantasy football
A pro-Texas Sen. Ted Cruz super PAC is using Florida Sen. Marco Rubio's own debate-prep spoof video against him, including it in an attack ad casting Rubio as unprepared for the presidency.
The only spoken words in the ad, airing on broadcast television in Iowa, come from Rubio himself, who jokes about setting his fantasy football lineup in the spoof video that Cruz's super PAC repurposed, saying: "Yeah I know I have a debate, but I gotta get this fantasy football thing right."
Rubio ties Christie to Obama
Rubio's super PAC is set to hit the New Hampshire airwaves Tuesday with two new spots targeting New Jersey Gov. Chris Christie -- who stands in the way of Rubio's effort to consolidate support from establishment Republicans, particularly in the Granite State.
The ads hit Christie over New Jersey's decisions to embrace Common Core education standards and expand Medicaid. "One high tax, Common Core, liberal energy loving, Obamacare Medicaid expanding president is enough," one ad's narrator says.
Santorum on Cruz's green eggs and ham
Cruz made headlines when, during a filibuster, he read the Dr. Seuss classic Green Eggs and Ham on the Senate floor. That footage shows up in a new ad airing in Iowa and paid for by former Pennsylvania Sen. Rick Santorum, who blasts Cruz's "fairy tales" in the Senate while playing up Santorum's foreign policy experience.
"Eight years on the Senate Armed Services Committee, helping to modernize today's Army to better be prepared for today's threats. Santorum also wrote and passed tough laws putting harsh sanctions on Iran," the narrator says.