Senator Charles Grassley last week linked the Boston bombing suspects to the fate of immigration legislation -- and now immigration-reform supporters are lashing out.

We should slow down reform, the Iowa Republican said, to make sure we are properly screening for terrorists. “Given the events of this week, it’s important for us to understand the gaps and loopholes in our immigration system,” Grassley said. “While we don’t yet know the immigration status of people who have terrorized the communities in Massachusetts, when we find out, it will help shed light on the weaknesses of our system.”

Today, Senate Judiciary Committee chairman Patrick Leahy rebuked Grassley. “Let me point out one thing that has troubled me a great deal,” Leahy said at his committee's hearing on immigration. "Last week opponents of comprehensive immigration reform began to exploit the Boston marathon bombing."

As demagogy goes, Grassley's remarks were pretty light stuff, no different in kind from gun-control advocates eagerly awaiting news on the origins of the bombers' arsenal in order to advance their own agenda. If it turns out that the bombers got their guns at a gun show, does anyone think gun-control advocates won't exploit that fact?

So Grassley deserves a pass on this one. What might merit condemnation are his comments about the modest background-check bill, promoted by two solid conservatives, which he helped to scuttle in the Senate last week. The bill explicitly forbade the creation of a national gun registry. But Grassley argued that background checks are a slippery slope. When they fail, gun-control advocates will turn to gun registration. "When registration fails, the next move will be gun confiscation," Grassley said.

Even here, it's impossible to tell whether Grassley is demagoguing the issue or whether he belongs to the paranoid fringe that actually believes that the very same government that refuses to require background checks for felons and the mentally ill will prove willing -- and able! -- to confiscate a couple hundred million guns. In Grassley's defense, in other words, he could be delusional.

The real indictment of Grassley, and the one I've never stopped marveling over, was his 2009 comment to a roomful of Iowa constituents that they should "be afraid" of the health-reform legislation then in Congress because "We should not have a government program that determines if you're going to pull the plug on grandma."

Sarah Palin gave that infamous lie currency, but Grassley's repetition of it was arguably worse. Unlike Palin, Grassley was ranking member of the Senate Finance Committee. He had been personally engaged in negotiations over health-care reform with Senate Finance Committee chairman Max Baucus, who was desperately (and futilely) seeking Republican support. Did he really think the legislation contained death panels?

No, he did not.

Second, Grassley was a member of Congress himself. Did he think the politicians who surrounded him, who were as desperate for public approval as he was himself, could somehow adopt death-panel legislation and then blithely run for re-election on that record?

No, he did not.

Grassley lied. And the lie he told was especially outrageous and poisonous, implying that Congress was run by people who deemed it appropriate for government bureaucrats to actively decide that some citizens should die rather than receive medical care. How anyone in Congress, Democrat or Republican, could ever work with Grassley in any capacity is beyond me.

(Francis Wilkinson is a member of the Bloomberg View editorial board. Follow him on Twitter.)