Trump, the bombastic businessman, has emerged as the likely Republican presidential nominee, partly fueled by strong rhetoric against trade deals and China. Britain, meanwhile, will vote on a possible exit from the European Union, a decision that some argue could shake its economic growth and broader expansion in Europe.
David Zervos, chief market strategist at Jefferies, believes both Trump's rise and a possible "Brexit" could drag on investors' returns.
"The two big events for me are Brexit and the election. They really make it a tough trading environment," he told CNBC from the sidelines of the Milken Institute Global Conference in California.
Zervos said investors "should key off dollar strength." After a rally near the end of last year, the greenback has lost nearly 6 percent this year against a basket of currencies.
That drop, he argued, "saved most people's portfolios" after a brutal start to the year for stocks. Oil prices, U.S. equities and some emerging markets have since stabilized. U.S. crude prices are up 7 percent this year, while the has climbed nearly 8 percent in the last three months.
While "it's off the table now," dollar strength could return, Zervos contended.
A Trump nomination after the GOP convention in July, or a surge in popularity, could fuel fears about trade, he said. That may drive nervous investors to the dollar.
Meanwhile, a British exit from the EU could sap confidence from the union. It may send some investors away from the euro and into the dollar, driving the greenback higher.
A Brexit brings the possibility of parity between the euro and the dollar, Zervos said.