Supposing honesty is the best policy, we should probably start here: For Rick Perry, Tuesday night's GOP debate is do or die.

The Tuesday evening forum at Dartmouth College in New Hampshire will allow the Texas governor to either redeem himself -- which, if his previous debates have anything to say, isn't particularly promising -- or continue on his downward spiral, threatening his candidacy. The New Hampshire debate will be Perry's fourth since getting into the GOP race, and as his numbers to continue to plummet, might prove to be his most important.

For months, the race has been focused, seemingly, squarely on the rivalry between Perry and former Massachusetts Gov. Mitt Romney. And while Romney, in Tuesday's Washington-Post-ABC News, maintains the lead, Herman Cain has risen from the bottom of the pile to give Perry a run for his money.

Romney Still on Top, But Cain Surging

In the poll, Romney held the lead with 25 percent of support among Republican voters, and Perry and Cain tied for 16 percent. But while you might wonder why we're talking about it: Perry has dropped 13 percentage points since the last Washington Post-ABC News poll last month; Cain has steadily risen 12 percentage points.

Furthermore, Perry's support has fallen precipitously among his base. Only 10 percent of Tea Party supporters back him now, compared to 45 percent last month. Among conservatives, his support has dropped from 39 percent to 19 percent.

Nearly all of his lost support has gone to Cain, the former Godfather's CEO who is running on a job-creating, businessman platform, as the International Business Times' Maggie Astor pointed out.

What is most debilitating, perhaps, for Perry is that in the last few weeks he has become known as a bad debater. This is critical, as voters can only decide to choose based on what a candidate says. It goes without saying that what a candidate utters should be what a candidate believes. And if he's unable to defend what he believes with the words he chooses to say, it gives the appearance of either not believing what he says or not knowing what he believes. So Perry has a lot of (good) talking to do Tuesday night. (It is for this reason that Cain has seen an uptick in popularity. He always says what he means and means what he says, however inflammatory it is.)

As Politico's, Jonathan Martin pointed out, Republicans actually knew very little about Perry when he jumped into the race. So, for now at least, he's being judged chiefly on the debates - events that for most party activists are their sole introduction to the candidate, Martin wrote.

Perry will be in the spotlight because he has to put on a better performance, said Fergus Cullen, former chairman of the New Hampshire Republican Party. The last few debates started to peel back the layers of the onion on Perry - and he really hasn't held up well.