Sergey Kislyak, Russian ambassador to the United States, is emerging as a key point of contact for members for the Trump campaign and Russia, and a reminder of the president’s ties to Vladimir Putin.

CNN reports that Kislyak is known to US intelligence officials as a spy recruiter. And that’s why he’s a touchy subject for Trump’s people.

Here’s a timeline of what we know about contacts between the Trump campaign and Kislyak: