“We are here to assure Donald Trump that there is nothing to be afraid of,” Ms. Stein said during a news conference and rally with his tower as a backdrop. “If you believe in democracy, if you believe in the credibility of your victory, put down your arms, end your bureaucratic obstruction, end your intimidation.”

The president-elect, who has raised his own doubts about the election, including his claim without evidence that “millions” of people voted illegally, has chided the recount effort. On Sunday, he went on Twitter to celebrate the setback in Pennsylvania, calling the bid a “Stein scam to raise money.”

Representatives of Mr. Trump did not respond to requests for comment on Monday.

Ms. Stein raised more than $7 million for the recount costs, as some supporters of Hillary Clinton have seen the effort as a last hope to change the outcome of the Nov. 8 election. Mrs. Clinton’s campaign has played a passive role in the process, acknowledging that the margins in the three states are too much to overcome.

Kellyanne Conway, a senior adviser to Mr. Trump, said on “Fox News Sunday” that Ms. Stein should “give it up.” Ms. Conway said, “Even your friends in the Clinton campaign have admitted that these recounts will not change any results.”

But instead, Ms. Stein seemed to be redoubling the effort on Monday with just two weeks remaining before the Electoral College is set to meet and install Mr. Trump. Mrs. Clinton would need to be named the winner in Michigan, Pennsylvania and Wisconsin to reverse the outcome of the election.