He just isn't all that good at this. And he knows it.

There's no other conclusion that you could draw after watching Jeb Bush flail in Wednesday night's Republican presidential debate. Bush looked overmatched and lost — an image made all the worse by the fact that he was positioned on the stage in Boulder, Colo., next to Marco Rubio, his one-time political mentee but now quite clearly his superior in the race.

Bush's attempt to attack Rubio was a metaphor not only for his debate performance but for his campaign. Knowing he needed to land a clean punch on Rubio, Bush piggybacked off a question from the moderators about Rubio's sparse attendance record in the Senate and tried to attack. But Bush doesn't really like attacking. And he backed into it from the start. “Could I bring something up here?” he asked, before somewhat awkwardly and, if I'm being honest, nervously, said this of Rubio: “I expected that he would do constituent service. Which means that he shows up to work.”  Then Bush, in an obviously prepared line, joked that Rubio was following a "French work week." (Ugh. Sad trombone.)

Rubio, ready for the hit, calmly dispatched a series of facts — including that John McCain missed lots and lots of votes in 2008 and Bush still backed him — before delivering this howitzer: “The only reason you are doing it now is because we are running for the same position, and someone has convinced you that attacking me is going to help you.”

The crowd cheered. Bush folded his hands and tried to respond. It didn't work. It was over — in more ways than one.

Dating all the way back to more than a year ago when it became clear that Bush was considering running for president, the question that I — and lots of other people — had was whether he really had the heart for it. Bush, even once it became clear that he was running, made clear that he had little love for the spectacle of the modern political campaigns and that he would do everything he could to avoid engaging in it. Bush knew then that he would never be the most charismatic candidate and wouldn't win the "beauty show" side of the race but believed that his policy smarts and the size and depth of his establishment support would win out.

Once the campaign began in earnest, however, it became clear that Bush was more than just rusty from having not run a campaign in more than a decade. He was simply underwhelming at every turn.  In each of the first two debates, while far less experienced pols such as Rubio, Donald Trump, Carly Fiorina and Ted Cruz outshone Bush, his allies sifted through the scraps of the debate in search of signs of life. He said his brother had kept the country safe! He was the grownup on stage!  They insisted that Bush just needed to keep improving in each debate. He would never be the performer that Rubio and Cruz are but he didn't have to be. He was Jeb, after all.

Those voices went silent after his flop in Boulder. (Sidebar: When your best argument is that you didn't get enough time to talk and your last name is "Bush," you are losing.) There is simply no way to spin what happened. Bush tried to do what his advisers told him he needed to. It didn't work. In fact, it backfired badly. He spent the rest of the debate in the shadow of that failure.

The question for Bush now is whether he really wants this — and, if so, how badly. His comments from over the weekend in South Carolina seem to reveal where his mind is. "I’ve got a lot of really cool things I could do other than sit around, being miserable, listening to people demonize me and feeling compelled to demonize them," Bush said. "That is a joke. Elect Trump if you want that."

It's hard to imagine Bush's outlook is any better after what happened to him Wednesday night. And, the coming days are likely to make things worse. Bush will be dogged by questions about his poor performance and news stories about donors either carping or bolting to Rubio — or both.

If Bush wasn't having much fun before, he really won't be having any fun now. And for a candidate who pledged that he would run "joyfully," he looks anything but that right now.