Presumptive Republican nominee Donald Trump is going to be the next president of the United States, and things could get "pretty scary" in the short-term, according to Jeffrey Gundlach , chief executive officer of DoubleLine Capital.

Still, investors should look at any Trump-related market downturn as a buying opportunity, he said.

Gundlach, speaking with CNBC on Friday, emphasized that he does not support political candidates, but his analysis leads him to believe Trump — who lags presumptive Democratic nominee Hillary Clinton in recent national polls — will win the White House.

"People aren't getting along, they're not happy because of technology taking jobs, and sort of this long, slow grind of a new economy. And so they're looking for change, and I think Trump is going to win on the basis of that," Gundlach said on " Fast Money Halftime Report ." "And he will be quite a bit like Ronald Reagan."

From a trading perspective, Gundlach said Trump is "bonds negative and stocks positive." And if Clinton were to win, she would mean the opposite for the markets, he added.

In fact, the fear surrounding a potential Trump presidency could be an opportunity for investors.

"Things are going to get pretty scary, and I think it's going to present quite a good buying opportunity because I think when Donald Trump is inaugurated, I think that he's going to initiate a very large deficit spending program," Gundlach said.

Such a program, he said, would probably not be "very prudent from a structural point of view," but would appear in the short term to be "working." Specifically, he said, a Trump-led domestic works program could both increase the deficit by $500 billion and bump GDP growth by 2.5 percent.