A new poll of Iowa shows Sen.(R-Iowa) with just a 1-point lead over his Democratic challenger andwith a double-digit advantage onin the presidential race.

While the gap closes in the Loras College poll when third-party candidates are listed, it suggests Trump, the presumptive GOP presidential nominee, faces an uphill climb in the Hawkeye State and that he may be hurting the six-term Republican senator.

Clinton has 48 percent support to Trump’s 34 percent in a head-to-head match-up.

When Libertarian Party nomineeand Green Party candidate Jill Stein are added, Clinton's lead narrows. In that scenario, she has 44 percent, with Trump at 31 percent, Johnson at 6 percent and Stein at 2 percent.

General election polls in Iowa are sparse, but a Public Policy Polling survey earlier this month gave Clinton a 2-point lead over Trump.

“I think third-party candidates, especially libertarian Gary Johnson, have their sights set on having 2016 be a breakthrough year. Both Johnson and Stein seek to capitalize on voter dissatisfaction and the lack of widespread enthusiasm of the Democratic and Republican candidates,” said Christopher Budzisz, director of the Loras College Poll.

The Senate poll shows Grassley with 46 percent support and Democratic challenger Patty Judge with 45 percent.

The tightening of the race comes as Grassley, the head of the Senate's Judiciary Committee, and his fellow Republicans continue to refuse a hearing for President Obama's Supreme Court nominee, Merrick Garland.

Budzisz noted that despite the poll result, Grassley would not be an easy person to take down in November.

“Senator Grassley is something of an institution here in Iowa, but Democrats are hoping to use his refusal to hold a Senate hearing on President Obama’s Supreme Court nominee against him," he said.

"I think they are also hoping for a negative down-ballot effect created by Trump as the presidential nominee. Senator Grassley will not be easy to unseat, however."

While the poll shows the results of the race are close, 70 percent of those surveyed said they expect Grassley to win.

"Still, in this volatile year, Senator Grassley appears to be facing a tougher challenge than most people would have predicted earlier this year," Budzisz added.

Public Policy Polling survey from earlier in June showed Grassley with a 7-point lead over Judge.

"The game has changed, folks — and it's because McConnell decided to block Garland," he tweeted

The Loras College poll surveyed 600 likely voters from June 24-28 and has a margin of error of plus or minus 4 percent.

—Updated at 2:57 p.m.