It looks pretty bad for former National Security Adviser Mike Flynn. His decision to invoke his Fifth Amendment privilege and not testify before Congress makes a lot more sense in the light of the letter that House Oversight Ranking Member Elijah Cummings released this afternoon.

Flynn may have failed to disclose -- or more accurately, lied about -- at least one source of foreign income. According to Cummings' letter, while seeking to renew his security clearance in February 2016, he apparently claimed that money he received from the Kremlin propaganda arm Russia Today actually came from American sources. There's also the issue of his failure to register as a foreign agent while doing work for Turkey's government.

Current and foreign officials with security clearances who take foreign money are required to disclose the payments, and certainly forbidden to lie about them.

Cummings tries to take this in the direction of the White House: What did they know, and when did they know it? If they knew anything -- or more specifically, if Trump knew anything at any point -- then his blind spot for and unwarranted loyalty toward Flynn is even more of a disastrous weakness than anyone could have imagined.

It's nearly impossible to believe that a president would knowingly choose someone compromised in this way as his NSA, if only because there's no way people wouldn't soon find out about it. And perhaps, as something nearly unthinkable, it's also unlikely. But Trump has a way of making the unlikely likely. After some of the things he said and did during his campaign, only to win, can anyone really say that anything is impossible anymore?