As investors pivoted quickly after Donald Trump’s election victory, their go-to was exchange-traded funds.

New York-based brokerage firm Convergex saw clients trading almost three times more ETFs on Wednesday, the day after the election, than they did on Tuesday while overall share trading rose 50%, according to Chief Executive Eric Noll.

“In times of market stress, traders and institutions have to adjust their portfolios quickly. The easiest way for people to refocus their portfolios without picking individual stocks is ETFs,” said Mr. Noll. “We’ve seen this trend developing over the past couple of years and it is really picking up steam now.”

Almost 3.2 billion shares of exchange-traded funds changed hands Wednesday, more than double the usual volume, after Mr. Trump’s unexpected victory. Traders and investors placed bets via ETFs on markets expected to be influenced by his administration’s regulations, trade policy and spending.

Mr. Trump’s pledge to repeal financial regulations imposed by the Dodd-Frank Act pushed up trading Wednesday in State Street Global Advisors’ Financial Select Sector SPDR Fund to $5 billion, the most in five years. His promise to dismantle the Obama administration’s Affordable Care Act propelled $756 million of investor flows into the iShares Nasdaq Biotech ETF on Thursday, the most in the fund’s history, according to FactSet.