An ad circulating online could be one of the nastiest slams against Barack Obama yet to surface. Run by the conservative National Campaign Fund, it attempts to blame the one-time Illinois state senator -- who supported Chicago's handgun ban and denounced the state's capital punishment procedures -- for three 2001 Chicago murders. The ad then asks: "Can a man so weak in the war on gangs be trusted in the war on terror?" (Video after the jump.)

The allegation of causality in these ads is ludicrous, to say the least. For one, the evidence that capital punishment is a deterrent to violent crime is shaky at best. And in Illinois, the state's death penalty laws were notoriously fraught, which Obama himself helped reform while in the statehouse. Thirteen people were released from death row because evidence had turned up that proved they were innocent or that their convictions had been tainted, leading to a justifiable moratorium that still stands.

Secondly, Chicago's murder rate actually declined while Obama was in Springfield, dropping from 789 homicides per 100,000 residents in 1996 to 448 in 2004. Attributing the drop to Obama's legislative efforts doesn't tell the whole story, of course; but the policies he and his colleagues pushed certainly didn't hurt.

Of course, this ad wasn't designed to present a rigorous analytic argument. It was created by Floyd Brown, the man responsible for the reprehensible "Willie Horton" ad against Michael Dukakis in 1988. Every four years, Brown resurfaces to sling his cheap, fearmongering attacks while Republicans stand idly by, quietly denouncing the spots but declining to intervene with any ferocity. Salon's Joe Conason suggests that "McCain must tell the Republican faithful, including the high-rolling donors who may finance Brown's advertising, that he is a pariah -- and that anyone who underwrites that kind of campaign will be unwelcome in a McCain White House." After this past month, such a statement would be valuable, but doesn't seem likely.

You can read more about Brown and the Vast-Ring Wing Conspiracy to which he ascribes at Fight the Smears.

Here's the video of the ad: