Steve Forbes sees Trump-Ryan meeting as a turning point in the presidential race

Will GOP unite behind Trump?

Now that Donald Trump is the presumptive GOP presidential nominee, the brash billionaire needs to refine his approach in preparation for the general election and avoid making off-the-cuff statements, said media mogul Steve Forbes, a two-time GOP presidential candidate.

But Trump's meeting last week with House Speaker Paul Ryan was a step in the right direction, added Forbes.

"[Trump] has got to change his campaign game plan, in the sense you just can't toss off comments anymore," the chairman and editor-in-chief of Forbes Media told CNBC's "Squawk Box" on Monday.

Forbes was responding to two statements Trump made in a CNBC interview earlier this month — one involved Trump saying his across-the-board tax cut may result in the rich paying more; the other was centered on Trump's remark about the national debt.

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The debt comment was widely debated, with some analysis saying Trump was advocating renegotiating with creditors.

Trump told "Squawk Box" in a phone interview on May 5: "I would borrow knowing that if the economy crashed you could make a deal. And if the economy was good, it was good. Therefore you can't lose."

But when pressed, he said: "There are times for us to refinance, refinance debt with longer term. ... I could see long-term renegotiations where we borrow at long-term at very low rates."

He further clarified his statements by saying: "I don't want to renegotiate [government-issued] bonds. I think you can do discounting. I think, depending on where interest rates are, you can buy back."

During that appearance, Trump argued for low rates to keep the national debt of $19 trillion somewhat manageable. Calling himself "the king of debt" in his business dealings, he warned the national debt would be troublesome if the cost of borrowing increases.

Trump's tax comment about rich paying more, which he subsequently made in variations elsewhere as well, was walked back. Trump said last week the wealthiest Americans might simply get a smaller tax cut than Trump originally proposed.

In a sign that Trump is incorporating more traditional methods into his unconventional campaign, Forbes pointed to Trump's meeting in Washington last week with Speaker Ryan.

"It shows Trump knows he's got to bring this party together," Forbes said, adding he believes Trump would not even thought about such a meeting just a few weeks ago.

Trump and Ryan released a joint statement after their Thursday meeting, which read in part: "We will be having additional discussions, but remain confident there's a great opportunity to unify our party and win this fall."

Following the meeting Ryan, who said the previous week he was "not ready" to support Trump, said the real estate mogul was "very warm and genuine." But Ryan did not endorse Trump.