If Mitt Romney is the Republican presidential nominee a year from now, it will be in part thanks to one of his primary rivals — Herman Cain.

In the most recent Washington Post-ABC News poll, the former Godfather’s Pizza CEO is tied for second place with Texas Gov. Rick Perry at 16 percent — a 13-point drop for Perry and a 12-point rise for Cain since early September. Romney is once again in the lead with 25 percent of respondents’ support.

Former Massachusetts Governor Mitt Romney (L) and businessman Herman Cain share a laugh before the start of the Orlando, Florida presidential debate. (SCOTT AUDETTE/REUTERS)

“Campaigning in a multi-candidate primary is like playing three-dimensional chess, where your biggest threat isn’t necessarily the one right in front of you,” said Republican strategist Todd Harris. “If I were in Boston I’d be singing ‘9-9-9’ all day long.” Harris is referring to the catchy tax reform plan championed by Cain that would set personal income, sales and capital gains taxes at 9 percent each.

Perry easily overtook Rep. Michele Bachmann (R-Minn.) when he got into the presidential race, and her campaign has done nothing but stumble ever since. Former Pennsylvania senator Rick Santorum has never taken off, and is counting on his conservative credentials to at some point catch fire.

In debates, Cain hasn’t piled on Perry the way other candidates have, making him seem somewhat above the fray. But in other appearances, he’s effectively raised doubts about Perry.

On CNN recently, Cain said that if Perry was the nominee today, he could not support him “for a host of reasons. Him being soft on securing the border is one.” Cain said on Fox News that Perry “was not up to primetime” in the last debate. He called the racial slur on a rock at Perry’s hunting camp “insensitive” (although he later walked that comment back, saying, “They painted over it.

Even if Cain collapses, as Bachmann did, enthusiasm for his campaign has delayed consolidation around Perry and exposed that candidate’s weaknesses. With New Jersey Gov. Chris Christie out of the race, no one is competing with Romney for moderate Republicans.

Cain himself might not be too upset with that outcome. While he’s been a frequent critic of Romney on the trail, he endorsed the tenuous front-runner in 2008.