Why would they be unable to develop sources on the inside? I don't think the pentagon press briefing area is where they would develop their sources regardless of being allowed in or not.
The inside of the pentagon is probably the worst place to ascertain honest and damaging information about the government.
The most famous of such sources, deep throat, refused to talk about information in the office or on the phone. Instead he would meet in an underground car garage.
This seems imminently sensible if you are disclosing damaging information about powerful and dangerous people doing illegal or immoral things. You’re not going to chat about it in the hallways at the pentagon.
In fact by creating an atmosphere of fear and paranoia through political persecution of the federal workforce they’re going to invite this sort of behavior. People are going to feel afraid and hide their beliefs but will need an outlet. The only reason to persecute people for their political beliefs and lock down transparency is to hide things that people unaligned to your ideology might disclose. They will still be there no matter what you do, they will just go underground in their behavior and take elaborate routes to tell what’s going on - and there will a lot to tell because it’s being hidden for a reason.
The more they dismantle oversight the more violation of ethics and legal requirements will happen - there’s no reason to dismantle the oversight functions unless you have things to hide. The more outrageous it comes, the more flagrant, the more those with discontent and grievance will seek out the press. (Surely there are some people in the government unhappy with how they or their (former) coworkers have been treated by this administration).
This is going to be the most spectacular case over over reach and hubris in our history and the blowout will be extraordinary as it unfolds and collapses around them, and I hope this will revitalize the independent press and investigative journalism - which frankly is not doing poorly already despite perception. There’s a lot of excellent outlets out there. And now increasingly major outlets are becoming independent of government influence once again.