This is a reasonable question. I have seen it reported that it is routine to tap, or monitor the phone traffic, of all foreign “high interest” targets. The Russian ambassador would be such a person, but recording the conversations of American citizens is supposed a complicated process. In this case, Flynn is a political figure, so you would think the judiciary oversight and sensitivity would be even greater.
It is hard not to see the intelligence leaks as a response to Trump’s remarkable hostility towards the CIA right after the election. I think trump is a disaster, but I’m not willing to cheer on CIA or other intelligence agencies while they try to discredit a democratically elected president.
This is ugly. If I ran the world, I would tell everyone to take a deep breath and let the Senate Intelligence Committee conduct its investigation. If there is any stonewalling by the administration or Republican members of the committee, then I would push for a special prosecutor.
If we can’t trust the wisdom and functioning of the United States Senate, then we are fucking done anyway. I may not like John McCain, James Cornyn, and Marco Rubio, but I am confident they will do their duty and protect the interests of the United States. They are not traitors.