"The voters in Iowa are making their frustration with Senator Grassley's obstruction clearer than ever,” said Amy Brundage, a spokeswoman for the Constitutional Responsibility Project. | AP Photo Poll: Supreme Court blockade eroding support for Grassley

Democrats are preparing another round of attacks against Senate Judiciary Committee Chairman Chuck Grassley, releasing new poll numbers that show the veteran Iowa senator’s favorability ratings are tumbling as he plays a key role in blocking Merrick Garland’s nomination to the Supreme Court.

The new poll, commissioned by the White House-aligned Constitutional Responsibility Project and the League of Conservation Voters, shows that more Iowans still have a favorable view of Grassley than not, with 42 percent of voters having positive feelings towards the senator and 30 percent having negative perceptions of him.


But those figures, obtained by POLITICO in advance of their release, are a steep dive from the numbers Hart Research Associates — which conducted Monday’s poll — found two years ago. Back then, 60 percent of voters gave Grassley a positive rating and 19 percent had a negative view.

“The voters in Iowa are making their frustration with Senator Grassley's obstruction clearer than ever,” said Amy Brundage, a spokeswoman for the Constitutional Responsibility Project. “This recess and going forward, we will continue to focus on exposing his failure to fulfill his constitutional responsibility until he gives Chief Judge Garland a fair hearing and an up-or-down vote.”

Grassley has long defended his opposition to taking up Garland’s nomination this year as a principled position that allows voters in November to help shape the direction of the court. Just two Senate Republicans out of the 54-member conference say Garland deserves a prompt hearing, and the likelihood of Garland getting a confirmation vote this year dwindles by the day.

“We have a unique opportunity for the American people to have a voice in the direction of the Supreme Court,” Grassley said last month. “Our side believes very strongly that the people deserve to be heard, and they should be allowed to decide, through their vote for the next president, the type of person who should be on the Supreme Court.”

A spokeswoman for Grassley dismissed the poll's results, calling them "selective."

“Selective leaks from a partisan group with a partisan agenda makes you wonder about what else they learned," Grassley spokeswoman Beth Levine said. "The White House and its paid political activists are trying to manufacture interest where it’s clearly not a defining issue. And, frankly, if polling actually made a difference to this White House, then Obamacare would be repealed by now.”

But the Hart Research poll argues that Grassley’s position could siphon off support for him this fall. According to the figures, one in five voters who said they might otherwise be inclined to support Grassley could be persuaded to vote against the senator because of his Supreme Court stance.

Overall, 57 percent of voters in the Hart poll said they support Garland getting a hearing and a confirmation vote this year, while 35 percent say filling the seat of deceased Justice Antonin Scalia should wait until a new president takes office next January.

Along with the numbers, the pro-Garland group released a video featuring two nurses from Iowa who said they traveled to Washington, D.C., to meet with Grassley and persuade him to take up Garland's nomination this year.

Grassley is still favored to win reelection, despite running in a purple state that President Barack Obama won in both 2008 and 2012. In 2010, Grassley won with 64.4 percent of the vote. Still, the longtime Iowa senator has candidly acknowledged that his reelection for a seventh term is his toughest yet.

The Supreme Court has been a hot issue at Grassley’s town halls throughout Iowa. But Washington’s focus on Garland has quieted somewhat since his nomination was first announced in March, and Grassley said recently that the Supreme Court fight hasn’t taken away from other initiatives in the Senate, such as an ambitious criminal justice reform effort.

“In fact, I think you’re seeing the Senate being more productive now than it has in a long time,” Grassley said. The Supreme Court issue takes away attention only when “meeting with Garland and answering our mail and answering our phones and answering questions from constituents.”

Former Iowa Lt. Gov. Patty Judge is challenging Grassley, but first she has to survive a crowded Democratic primary. The poll released Monday surveyed 400 Iowa voters and was conducted from April 22 to April 24.

Burgess Everett contributed to this report.