The timing of the latest Rasmussen poll may be the most interesting part of the report.  Herman Cain got his toughest grilling in a national debate on Tuesday, October 18th, and yet the next day, Cain led among likely Iowa caucus-goers by seven points over Mitt Romney.  The Iowa electorate may be firming up their choices, too:

A new Rasmussen Reports telephone survey of Likely Iowa caucus-goers shows that Cain is in front with 28% followed by former Massachusetts Governor Mitt Romney at 21%. Congressman Ron Paul is a distant third at 10% followed by former House Speaker Newt Gingrich at 9%, Congresswoman Michelle Bachmann at 8%, and Texas Governor Rick Perry at 7%. The sixth place finish for Perry is a sharp decline from early September when Perry was the frontrunner both nationally and in Iowa. (To see survey question wording, click here).

Former Senator Rick Santorum picks up 4% of the vote and former Governor Jon Huntsman is at 2%. Another 4% would prefer some other candidate and 8% are not sure.

Only one-third of the caucus-goers (32%) are certain of their vote and don’t expect to change their mind. Among these voters, 30% prefer Cain, 22% Romney, and 17% Paul.

Cain didn’t have a great debate on Tuesday, but didn’t get rattled, either.  His 9-9-9 plan took more than a few hits, and Cain had to reverse his answer to Wolf Blitzer earlier in the day on negotiating with terrorists and conducting prisoner swaps.  So far it doesn’t appear to have hurt him, but it’s also possible that those issues may take more than a day to manifest themselves as big problems.  This polling also took place before Cain’s confusing answer on abortion last night on CNN, which will not play well at all in socially-conservative Iowa.

The crosstabs show a solid lead across most of the survey’s demographics.  Cain leads Romney among men and women outside the margin of error, as well as voters under the age of 65.  Cain edges Romney among Republicans but nearly doubles up Romney among independents, 28/15, a big problem for Romney if that trend continues.   Romney does lead among self-professed liberals, 20/14, and gets within the MOE with moderates, 23/21 Cain.

Rasmussen also runs the numbers for a three-person race in the primary, and Cain does even better, beating Romney by nine at 40/31 with Perry trailing far behind at 13%.  Interestingly, when Rasmussen takes Perry out and puts Cain and Romney head to head, the polling narrows to a 5-point Cain lead, with Romney tying Cain among women.  That’s an early indication that Perry may not have gotten much of a bounce coming out of his debate performance on Tuesday, or that it may take more than one not-too-bad debate to change minds on his chances.  With about eleven weeks left to go before the caucuses, Perry doesn’t have a lot of time to make the case a second time to carry the banner for Republican conservatives.

This poll isn’t bad news for Romney, either.  Despite having not made Iowa a campaign priority, Romney is poised for no lower than a second-place finish — and could end up winning if Cain implodes.  A second-place finish would give Romney plenty of momentum going into New Hampshire and Nevada, where he’s widely expected t win big, with both Michigan and Florida on the horizon.  If Romney wins Iowa, it will be a lights-out moment for the rest of the field, as Republicans will want to start gearing up to fight Obama as soon as possible.