After a student leader of the historic Tiananmen Square protests entered a 2022 congressional race in New York, a Chinese intelligence operative wasted little time enlisting a private investigator to hunt for any mistresses or tax problems that could upend the candidate’s bid, prosecutors say.

“In the end,” the operative ominously told his contact, “violence would be fine too.”

As an Iranian journalist and activist living in exile in the United States aired criticism of Iran’s human rights abuses, Tehran was listening too. Members of an Eastern European organized crime gang scouted her Brooklyn home and plotted to kill her in a murder-for-hire scheme directed from Iran, according to the Justice Department, which foiled the plan and brought criminal charges.

The episodes reflect the extreme measures taken by countries like China and Iran to intimidate, harass and sometimes plot attacks against political opponents and activists who live in the U.S. They show the frightening consequences that geopolitical tensions can have for ordinary citizens as governments historically intolerant of dissent inside their own borders are increasingly keeping a threatening watch on those who speak out thousands of miles away.