The stock market has recently been looking less certain about a Hillary Clinton victory in November, according to a new report by Strategas Research Partners.

"The market has been pricing in a closer election all summer. And now the polls are starting to catch up with what investors had been sensing in the month of August," Strategas' Dan Clifton told CNBC's "Squawk Box" on Friday.

During election cycles, Strategas puts together two different portfolios, aiming to reflect which stocks would do well if the Democratic presidential nominee wins in November and which stocks would benefit from a GOP victory.

"The Democratic portfolio is outperforming the Republican portfolio by about 3 percent year to date," said Clifton, head of policy research.

But that gap has been narrowing, he added. "At one point, the Democratic portfolio was outperforming the Republican portfolio by 10 percent."

Clifton said the Democratic portfolio peaked on July 5, the day the FBI released its findings on Clinton's use of a private email server when she was President Barack Obama's secretary of state and recommended no criminal charges be filed.

"Slowly the Republican portfolio has been outperforming [since then]," he said, though pointing out the 86 percent correlation between the S&P 500 and Clinton's probability of winning the election.

Sectors that might benefit from a Clinton win include health care, "not including pharmaceuticals," because Democrats would keep Obamacare in place but would also take a harder line against drug-price increases, Clifton said.

Infrastructure spending should increase under either a Clinton or a

Donald Trump presidency, but would likely go up more under Clinton, Clifton said.