No third-tier candidate had a better response to Fox News' announcement that it would only allow the top 10 candidates into the first Republican debate than Rick Santorum. Santorum noted that poll numbers might not accurately capture a candidate's viability. "In January of 2012," he said, "I was at 4 percent in the national polls, and I won the Iowa caucuses."

That's true. He was. And he did. Santorum went on to be a surprisingly strong candidate for the nomination, though obviously, an unsuccessful one. In the recent Republican tradition of runners-up getting the nomination during the next open cycle, it would seem that Santorum should be positioned for strength.

He isn't.

In polling published Tuesday by the The Post and ABC News, Santorum is running ninth -- and, rather ignominiously, is tied with Donald Trump. He trails Jeb Bush, Rand Paul, Scott Walker, Mike Huckabee, etc., etc.

He is at 4 percent, as he was before Iowa in 2012. But there's a big difference: Other candidates are vacuuming up the support he saw from critical constituencies.

Among conservative voters, Santorum ran just a bit behind front-runner Mitt Romney in an average of 2012 exit polls in early primary states. In Iowa, he ran ahead of Romney with conservatives.

In this most recent 2016 poll, he trails among conservatives with every candidate that's polling better than him except Bush, Chris Christie, Donald Trump and John Kasich.

In 2012, he led Romney among white evangelical voters by a large margin in Iowa. Now, he is tied for 10th.

We looked at the "lanes" theory of the Republican field in March. The idea is that candidates want to lock down a particular category of Republican voters to assure that they can stick around in the primary contest. In 2012, Santorum did a good job locking down evangelical voters in particular. This time, he hasn't — thanks to a much larger field with much stronger candidates.

Santorum's point was that miracles happen. That appears to be what he's going to need between now and January to win.