Back to Iowa, Trump faces some disgruntled independents

Unaffiliated voters make up the largest percentage of the electorate in the Midwest state that backed Trump in 2016, after lifting Democrat Barack Obama to the White House in party caucuses and two straight elections.

Self-identified independents in Iowa voted for Trump over Democrat Hillary Clinton by a 13-percentage-point margin last year, according to exit polls conducted for the Associated Press and television networks

In North Carolina, Republican pollster Paul Shumaker says he has seen internal polling that has warning signs for his state, where Trump prevailed last year.

Independent voters are becoming frustrated with Trump, especially for failing so far to deliver on long-promised household economic issues such as health care, said Shumaker, an adviser to Republican Sen. Richard Burr.

Inaction on health care and any notable decline in the economy will hurt Trump's ability to improve his numbers with independents, with broad implications for the midterm elections next year, Shumaker said.

Earlier this month, Vice President Mike Pence attended Republican Sen. Joni Ernst's annual fundraiser, where he talked about job growth and low unemployment since the start of the year, although economists see much of it as a continuation of Obama policies.