WASHINGTON — Senate investigators are scrutinizing links between Jill Stein, the Green Party’s 2016 presidential nominee, and Russia’s campaign to interfere in the 2016 presidential election, searching for evidence of possible conspiracy.
Senator Richard Burr of North Carolina, the Republican chairman of the Senate Intelligence Committee, said on Monday that the committee was “just starting” to look at Ms. Stein’s campaign along with another campaign, which he declined to name, as it continues its investigation of the Trump campaign. Mr. Burr has previously suggested the committee is looking at aspects of the Clinton campaign.
Democrats have seethed for more than a year at Ms. Stein, whose tens of thousands of votes in Michigan, Wisconsin and Pennsylvania either exceeded or nearly matched Donald J. Trump’s margins of victory in those states, which delivered him the White House. At least in certain quarters, they greeted news of the queries enthusiastically.
Jesse Ferguson, a former Clinton campaign spokesman, said Americans ought to know if a presidential nominee, no matter how minor, had become a Russian asset or was simply boosted in an effort to chip away Democratic votes from Mrs. Clinton.
“Russian operatives were not promoting Jill Stein because they thought she would win,” Mr. Ferguson said. “They were promoting her because they thought it would hurt Hillary Clinton and help Donald Trump.”
Ms. Stein confirmed late Monday that the committee had contacted her campaign to request documents, including emails. Such requests usually precede an interview with the committee. In a statement, she pledged to cooperate but warned against such inquiries being used to “intimidate and silence principled opposition to the political establishment.”
“We strongly support legitimate inquiry into any illegal activity in our elections — including quid pro quo deals, money laundering, corruption and violation of campaign finance laws,” Ms. Stein said. “At the same time, we caution against the politicization, sensationalism and collapse of journalistic standards that has plagued media coverage of the investigation.”
The Senate Intelligence Committee’s request to the Stein campaign was first reported by Buzzfeed News.
Senate investigators are interested in unraveling what was behind the apparent closeness between Ms. Stein, a Harvard-educated doctor and perennial Green Party candidate, and Russia.
Ms. Stein traveled to Moscow in 2015 for a dinner celebrating the tenth anniversary of RT, the state-run news organization that American intelligence agencies have concluded was being used to spread propaganda during the presidential campaign.
Photographs from the event show Ms. Stein sitting at a table with President Vladimir V. Putin of Russia and other prominent Russian government officials. Sitting across from her was another American, Michael T. Flynn, Mr. Trump’s former national security adviser who has now entered a plea agreement with Robert S. Mueller III, the special counsel investigating Russian election interference.
A year later, RT hosted the Green Party’s presidential debate, and showered attention on Ms. Stein’s campaign.
In her statement, Ms. Stein said she attended the 2015 dinner at her own expense in hopes of “reaching an international audience and Russian officials with a message of Middle East peace, diplomacy, and cooperation against the urgent threat of climate change.”
Also drawing scrutiny is Ms. Stein’s relationship with Julian Assange, the founder of WikiLeaks. Mr. Assange called in via Skype to the Green Party’s convention in August 2016 to discuss the hacked Democratic National Committee emails that were published by WikiLeaks. And Ms. Stein praised Mr. Assange as a hero for exposing the emails.