This story has been updated.

TAMPA — Jeb Bush kicked off the most critical two-week period of his presidential campaign so far with a Monday morning speech that aimed to draw a sharp distinction between his record as governor of Florida and the Senate resumes of his GOP rivals.

While he didn't single him out by name, Bush seemed to be implying a contrast with Sen. Marco Rubio (Fla.). Bush and Rubio have sparred more often in recent weeks, most notably at last week's debate. In a presentation to donors last week, Bush's campaign labeled Rubio a "GOP Obama."

“The answer isn’t sending someone from one side of the capital city to the other," Bush said at one point.

At another: “The challenges we face as a nation are too great to roll the dice on another presidential experiment."

Bush also appeared to take aim at Donald Trump, a frequent agitator.

“You can’t just tell Congress… ‘You’re Fired’… and go to a commercial break," said Bush.

With his speech, the former Florida governor launched his "Jeb Can Fix It" tour. He has been emphasizing his leadership credentials in hopes of distinguishing himself from Rubio and others.

[Jeb Bush gave this black community a charter school. Then he moved on.]

Lagging in the polls and coming off a widely panned debate performance, Bush plans to barnstorm the early voting states this week, moving from Florida to South Carolina and then embarking on a three-day bus tour through New Hampshire. Plagued throughout his campaign by distracting comments, Bush is in need of an error-free performance that amplifies his argument for the presidency: that his leadership credentials and record as governor best qualify him for the top job.

Then, Bush will need a strong performance in the fourth televised Republican debate next Tuesday. The next one after that is not until mid-December. Debates have not been Bush's strong suit so far. Whatever happens next Tuesday night could be etched into the minds of GOP primary voters for weeks.

“This election is not about a set of personalities," said Bush, decrying the last debate's focus on "sound bites." He added: "It’s about a set of principles. It's about leadership."

Bush's tour comes the same week he is releasing his e-book "Reply All," an exhaustive anthology of hundreds of self-selected e-mails he sent and received as governor.

Bush's large network of donors and other supporters is anxiously watching him this week. One Bush fundraiser, granted anonymity to speak candidly after last week's debate, said the campaign is running out of time to get things right.

"They keep trying to re-calibrate and reset and start over,” the person said. “I think you get one or two of those. They are at like number three."

Bush has acknowledged his struggles and is vowing to overcome them.

"Look, I know that I got to get better at doing the debate," he said in an interview broadcast Sunday on NBC's "Meet the Press." "I'm a grinder. I mean, when I see that I'm not doing something well then I reset and I get better."

Ed O'Keefe contributed to this report.