Mohamed El-Erian, chief economic adviser at Allianz, told CNBC last week that the U.S. market has not yet priced in the political uncertainty. Part of the reason for the delayed response is that traders and investors are having difficulty interpreting Trump's success.
"I think the hardest thing for the markets to assess — and that is why you don't see the premium — is, how do you have a front-runner that doesn't have the backing of his party?" El-Erian said.
As the competition for the Republican nomination drags on, Lafferty argues that the markets would grow even more skittish, in tandem with Trump's continued popularity.
"I think that as we get later in the year, as we get more results and we approach the convention, I think it's gonna weigh on the markets a little bit. It will weigh more on day-to-day volatility, the bumpiness of the market," he said, adding that the market could begin to see the effects starting in June.
In an email to CNBC, Lafferty said that while Clinton is seen as the likely winner of a head-to-head showdown in current polls, "the market could stumble badly this summer if Trump can close the gap." Lafferty added that Trump's "newcomer status will keep equities on edge if his chances improve in the coming months."
— CNBC's Bree Kelly and Katy Barnato contributed to this report.
Correction: This version corrects the name of the strategist's firm to Natixis Global Asset Management.