Once again, billionaire businessman Donald Trump is flirting with a run at the White House.

Trump, who teased bids in 2008 and 2012 but ultimately did not pull the trigger, spoke to a gathering of conservatives in Iowa on Saturday, and he said he's "seriously thinking about running for president, because I can do the job."

Trump was speaking at the Iowa Freedom Summit, a cattle call spearheaded by Rep. Steve King, R-Iowa, which has drawn a number of potential 2016 candidates to Des Moines.

In his remarks, Trump took square aim at two potential candidates for the 2016 GOP nomination who weren't in attendance, suggesting it would be an error for Republicans to nominate either 2012 GOP nominee Mitt Romney or former Florida Gov. Jeb Bush.

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"It can't be Mitt, because Mitt ran and failed," Trump said.

Trump said he liked Romney, formerly a governor of Massachusetts, but he suggested Romney's infamous "47 percent" comments and his affiliation with a Massachusetts health care reform plan akin to Obamacare should disqualify him.

Plus, Romney "choked" in 2012, failing to unseat Obama in an election that Republicans could have won, Trump argued.

"You can't have Bush," Trump added. "The last thing we need is another Bush."

Trump criticized Bush's support of common core federal education standards, and he panned Bush's comment that many illegal immigrants come to the United States as an "act of love" to help their families.

"Half of these people are criminals," Trump said. "They're coming for a lot of other reasons, and it's not love."

Trump also suggested the unpopularity Jeb Bush's brother, former President George W. Bush, helped usher President Obama into office: "His brother really gave us Obama."

Trump offered an ambitious preview of his prospective presidential agenda. " If I run for president, and if I win, I would totally succeed in creating jobs, defeating ISIS, and stopping the Islamic terrorists... reducing the budget deficit... securing our southern border... stopping nuclear weapons in Iran and elsewhere... saving Social Security, Medicare, and Medicaid without cutting it down to the bone... repealing Obamacare and replacing it with something far better."

Trump deviated somewhat from the GOP's fixation on entitlement reform, warning Republicans that "Democrats are eating your lunch on this issue."

He said he would not cut Social Security, because people deserve to receive the benefits they've earned, but he would bring the system back into solvency by making the U.S. "rich again."

Veteran political watchers have heard this all before from Trump, and there's ample reason to be skeptical that he would actually dive into the chaos of the Republican nominating process.

But several other potential candidates who are more likely to jump into the fray also spoke on Saturday. Wisconsin Gov. Scott Walker, for one, rallied the crowd as he recounted his push to limit the collective bargaining rights of public employee unions in his state and the effort to recall him from office that resulted.

His victory in the recall and his subsequent reelection, Walker argued, should send a message to fellow Republicans: "If you're not afraid to go big and go bold, you can actually get results... And if you get the job done, the voters will actually stand up with you."

Walker said the GOP must demonstrate "new and fresh and bold and aggressive" leadership if it hopes to take the White House in 2016.

And Dr. Ben Carson, a retired neurosurgeon and conservative activist, also lit up the crowd with a message focused on education and personal responsibility.

"Anybody who gets a good education can write their own ticket," Carson said, citing himself as an example. "The person who has the most to do with what happens to you in life is you."

He touched briefly on immigration reform, emphasizing the need to seal the border, and health care reform, saying it's "imperative that Republicans embrace a simple, effective system that puts people and their health care providers in charge of their health care."

Carson also urged the conservatives in the audience to "have courage again in this country."

"We cannot allow the progressives to shut us up," he warned.