The market rally following the November 2016 presidential election was bust for INTECH Investment Management LLC, according to Janus Capital Group Inc. CEO Richard Weil.

As equities steadily advanced, INTECH took a hit, causing the unit to become one of Janus' balance-sheet negatives for 2016 fourth-quarter and second-half results, Weil said during an earnings conference call. Janus' volatility manager experienced a downturn that lasted for five consecutive months, an unusually long slide that followed a strong first-half management performance, including immediately after the U.K.'s vote to leave the European Union.

"They had one or two of their best days after the Brexit announcement, and they had one or two of their absolute worst days after the [Donald] Trump election," said Weil.

The unit's underperformance was not shallow during the slump, but substantial, he told analysts and investors. But Weil does not think the outflows will get worse or that INTECH's investment strategy is wrong.

"I'm convinced that their process is still a very good process, [and] is still valuable for clients," he said. The company has had a tough time selling its products inside the U.S., he conceded, but has been more successful internationally.

Janus continues to expects its merger with Henderson Group Plc to close in the second quarter. Asked about the potential for a changed regulatory environment following the Brexit vote and Trump's election, Weil said the companies are still better off facing those uncertainties combined rather than alone.