It's not even a secret, look at the Tor Project's funding sources (public tax record). State Dept & DoD were their primary funders last time I checked.
Hypothetically, if the USG wanted to produce "official" backdoored TOR clients (e.g. only served as prebuilt downloads to IPs geolocated in Iran, etc to make detection difficult), they are in an excellent position to influence that work. And as the story of Julian Assange makes clear, that should concern anyone who purports to care about privacy, human rights, etc.
Hypothetically, if the USG wanted to produce "official" backdoored TOR clients (e.g. only served as prebuilt downloads to IPs geolocated in Iran, etc to make detection difficult), they are in an excellent position to influence that work. And as the story of Julian Assange makes clear, that should concern anyone who purports to care about privacy, human rights, etc.