Correction: Due to an editing error, the headline of this piece said the debate was Tuesday. Rest assured, today is Wednesday, and the debate is today.

Quick: Name a time in the 2016 campaign when Jeb Bush has outperformed expectations.

It's hard to do, right?  The only one that sort-of fits the bill was his speech to at the Conservative Political Action Conference in February. Bush faced down a tough crowd by using enthusiasm and conviction to explain positions where he and they disagreed.  You might be able to name one or two other speeches or appearances where Bush was marginally better than he was expected to be, but generally, his campaign has been defined by his lackluster performances in big moments; in both of the first two presidential debates, he was mediocre at best.

Which brings me to tonight in Boulder, Colo., where the third GOP debate will be held. The stakes for Bush are different -- and higher -- this time around. Unlike in the previous two debates, Bush comes into tonight's showdown wounded as a candidate following his decision to make significant salary cutbacks and spending reductions in the face of weaker-than-expected fundraising numbers over the past three months.

In short, the vultures are circling. Bush's entire campaign argument was centered on inevitability, but the nomination no longer looks so inevitable. Many of the people who signed on to his team — especially on the donor side — did so because they wanted to be with the guy they thought would be the winner. If Jeb doesn't look like that guy anymore, there will be a lot of people itching to jump ship.

Tonight's debate, which will air on CNBC starting at 8 p.m. Eastern time, is Bush's best chance to turn the "he's disappointing" narrative on its head. If the past two debates are any indication, the audience will be huge — well more than 20 million — and all eyes (or at least the smart eyes) will be on Jeb.  And, if you don't believe a single strong debate performance can drastically alter a campaign's arc, go back to Hillary Clinton's performance 15 days ago in the first Democratic debate.

How can Bush do it? By showing some life, some passion, some energy.  Truth be told, Donald Trump's attacks on Bush as "low energy" have hurt the former Florida governor because, well, he appears to be pretty low energy. And, his comments over the weekend in South Carolina, which amount to something like "I have a lot better things to do than running for president," suggest he might not be in the best mind space at the moment.

Bush needs to show he WANTS the Republican nomination and is willing to fight like hell for it. The problem for him -- and this has always been Jeb's problem -- is that he has always been a sort of awkward candidate, more suited to being governor (or president) than running for the office. He's not a natural emoter or fighter; he's an introvert who tends to be more reserved in public. All understandable. But all also part of the problem he currently has in this race where people just aren't sure how much he wants the job and, even more importantly, why he wants the job.

The CNBC debate isn't a make or break moment for Bush — remember that his super PAC still has massive sums left to spend on his behalf. But, he needs to start showing signs of life. And, soon.