Democrats are increasingly laying a hammer to Sen. Chuck Grassley Charles (Chuck) Ernest GrassleySenate Republicans face tough decision on replacing Ginsburg What Senate Republicans have said about election-year Supreme Court vacancies Biden says Ginsburg successor should be picked by candidate who wins on Nov. 3 MORE as they seek to unseat the Iowa Republican.

Grassley’s Senate seat is widely viewed as likely to stay in the GOP column, but Democrats believe the rise of Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE and the fight over the Supreme Court are providing the perfect storm for taking out the six-term GOP incumbent.

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Grassley has been perennially popular in his home state, where he's built a reputation as a GOP senator with an independent streak.

But a poll this week conducted by a Democratic-leaning firm for the Constitutional Responsibility Project found Grassley leading Democratic challenger Patty Judge just 48 percent to 41 percent.

It’s a margin far below Grassley’s past elections, when he’s frequently won at least 60 percent of the vote.

Republicans brushed off the poll from the left-leaning firm, but Judge’s campaign pounced on it to try to buy some momentum.

Sam Roecker, Judge’s campaign manager, said Grassley is “in a race unlike any other during his 36 years in the U.S. Senate” and that he’ll be held accountable “for his obstruction and inaction.”

Democrats are pitching to voters that Grassley has changed and is no longer a maverick independent always looking out for Iowa.

Instead, they want to paint him as working hand-in-hand with presumptive GOP presidential nominee Trump and Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE (R-Ky.).

Outside groups, Judge and Senate Minority Leader Harry Reid Harry Mason ReidGraham signals support for confirming a Supreme Court nominee this year Trump signals he will move to replace Ginsburg 'without delay' Senate Republicans signal openness to working with Biden MORE (D-Nev.) have been blistering in their attacks, particularly on Grassley’s role in refusing to hold a vote or a hearing for Merrick Garland, President Obama’s nominee to the Supreme Court.

The same poll showed presumptive Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE defeating Trump in Iowa, suggesting Grassley will have to hope voters split their ballots.

Grassley, like most Republicans, is planning to localize his reelection bid, telling a local radio station this week that going into November he would “continue to hold government accountable” and “legislate in a bipartisan effective way.”

Asked about the steady stream of criticism from Democrats, Grassley’s office pointed to a fact sheet focused on Reid’s arguments against Grassley. It is entitled “There's Reid, and then there's reality.”

The release, which replies to approximately two dozen comments from Reid, touts the dozens of bipartisan bills passed out of the Judiciary Committee under Grassley’s watch and states that if the State Department had answered his initial letters in 2013, the inquiry into Clinton's private email server wouldn’t have dragged on.

Republicans also downplay concerns that the Democratic attacks are making inroads with voters in Iowa, noting that after decades in politics, Grassley is a known quantity in his home state.

“[Grassley’s] broadly popular, even with Democrats, in Iowa. National Democrats have done nothing to change it,” said Greg Blair, a spokesman for the National Republican Senatorial Committee.

Democrats are trying to tie Grassley to Trump.

Judge's campaign released a web ad this week playing up a blistering Des Moines Register editorial that was critical of Grassley's response to Trump's assertion that U.S. District Judge Gonzalo Curiel has “an absolute conflict” in presiding over fraud lawsuits against Trump University because of his Mexican heritage.

The state’s largest newspaper wrote that “when it comes to Donald Trump, there are invertebrates that have shown more spine than Sen. Charles Grassley Charles (Chuck) Ernest GrassleySenate Republicans face tough decision on replacing Ginsburg What Senate Republicans have said about election-year Supreme Court vacancies Biden says Ginsburg successor should be picked by candidate who wins on Nov. 3 MORE.”

While more vulnerable GOP senators are trying to keep a safe distance or are disavowing him altogether, Grassley hasn’t shied away from talking about Trump.

He introduced the brash businessman at an Iowa rally earlier this year, told reporters that his list of potential Supreme Court picks should assuage the doubts of conservative voters, and is planning to attend at least part of the Republican Party’s national convention in Cleveland next month.

He also isn’t ruling out campaigning with his party’s likely presidential nominee.

“The answer is yes. I think that you ought to ask him if wants to campaign with me. If he asks me to campaign with him, I would,” Grassley told two Iowa reporters during a phone interview that was subsequently circulated by American Bridge, a Democratic super-PAC.

Grassley’s willingness to talk Trump has landed him in hot water, including last week when he had to clarify that he didn’t mean to “equate” Trump's racially charged attack against Curiel to a line Supreme Court Justice Sonia Sotomayor used in speeches about diversity.

But he also told local reporters that Iowans “aren’t very concerned” about Trump's comments on the district judge.

Democrats are betting that Grassley is wrong. Sen. Jon Tester Jonathan (Jon) TesterPence seeks to boost Daines in critical Montana Senate race This World Suicide Prevention Day, let's recommit to protecting the lives of our veterans Filibuster fight looms if Democrats retake Senate MORE (D-Mont.), the chairman of the Democratic Senatorial Campaign Committee, said he thinks it’s possible Grassley could lose.

“Not only his stand with supporting Donald Trump, but also the fact that he won’t give a hearing to a Supreme Court justice,” Tester told USA Today earlier this month. “That’s not Iowa; that’s not Iowa values.”