Democrat Zephyr Teachout officially opened her campaign for New York state attorney general on Tuesday, standing in the shadow of Trump Tower while emphasizing her mission to force President Donald Trump to ​divest himself from his businesses.

“We must litigate more aggressively,” Ms. Teachout said to a small crowd on the sidewalk near the high-rise. “The beating heart of Trump’s corruption is here in our state.”

Ms. Teachout, 46 years old, was one of the leading attorneys on a 2017 lawsuit, ultimately dismissed, brought against Mr. Trump by the nonprofit group Citizens for Responsibility and Ethics in Washington. The suit challenged the president’s business holdings and claimed he was in violation of the Constitution’s emoluments clause, which prohibits government officials from receiving gifts, payments, offices or titles from foreign states without approval from Congress.

Throughout his campaign and presidency, Mr. Trump has maintained he has no conflicting business interests. The White House didn’t respond to requests for comment Tuesday.

Former Attorney General Eric Schneiderman, a Democrat who resigned last month amid allegations of physical abuse, took more than 100 legal actions against the Trump administration during his tenure, including challenges to its travel ban, its repeal of the Clean Power Plan and changes to the Deferred Action for Childhood Arrivals program, or DACA.