Republican front-runner Trump repeatedly defended Lewandowski throughout a day of campaigning in Wisconsin.

The Republican front-runner's stumble in Wisconsin exposed a variety of weaknesses.

Republican front-runner Donald Trump has repeatedly questioned Cruz's eligibility because of his Canadian birth.

Republican front-runners Mitt Romney and Rick Santorum, for example, do not hold state or local office.

Republican front-runner Donald Trump has threatened to deport the 11 million already in the United States.

Others have not released fundraising numbers yet, including Republican front-runner Jeb Bush, a former Florida governor.

Complicating TPP's prospects in Congress are opposition from aspiring presidential candidates, including Republican front-runner Donald Trump.

The Republican front-runner could knock out his two mainstream rivals, Ohio Governor John Kasich and U.S.

Mr Trump - who did not actively campaign in the state - remained the Republican front-runner overall.

But the Republican front-runner came under attack from Marco Rubio who warned that what presidents say have consequences.

China has also come under fire from Republican front-runner Donald Trump, who accuses it of stealing U.S. jobs.

The Republican front-runner gained on Obama compared to last month, when he was behind by eight percentage points.

One reason for all that piano playing is the unconventional campaign being run by Republican front-runner Donald Trump.

Republican front-runner Donald Trump has repeatedly brought up questions about whether Cruz meets the constitutional requirement to be president.

But on the issue of climate change, he departed from some other potential Republican front-runners in the 2016 race.

It was a stark display of the divisions the Republican front-runner's presidential campaign has long been accused of sowing.