In “ How U.S. intelligence agencies can find out what Trump told Putin : A top-secret Special Collection Service has extraordinary capabilities to hoover up intel from foreign adversaries” (POLITICO) we learn that
“the only way they're (U.S. intelligence) learning about what was said in that closed-door meeting is through NSA reporting, top-secret code-word reporting, about what the Russians say was said in that meeting. And what the French foreign ministry and, insert other country here, think happened in Helsinki based on what the Russians told them."
“Obviously this is so crazy that no one thought this would happen,” Schindler said of the U.S. intelligence agencies’ scramble to figure out what, exactly, a sitting U.S. president said in a meeting with a known belligerent adversary. “The really important stuff from an intelligence viewpoint is what we collect on the meeting. But because there’s no U.S. version to check it against, the Russians could be lying about it and we wouldn’t even know.”
Politico reports that there’s an entity I’d never heard of until now, the Special Collection Service:
Because the summit was finalized just a few weeks beforehand, U.S. intelligence officials had to scramble to get their agents, analysts and technical collectors in position to eavesdrop on an event that had the potential of being one of the most consequential of Trump’s presidency, according to current and former U.S. officials. The Special Collection Service, the ultra-classified team of NSA and CIA interceptors, no doubt began moving into position as soon as the decision was made, they said.
The fly in the ointment is that Trump could have ordered the Special Collection Service of the United States not to engage in any intelligence gathering in Helsinki.
That does not mean that foreign intelligence agencies didn’ t gather intelligence prior to and following the meeting. This would have been in the nature of signals intelligence:
Signals intelligence (SIGINT) is intelligence-gathering by interception of signals, whether communications between people (communications intelligence—abbreviated to COMINT) or from electronic signals not directly used in communication (electronic intelligence—abbreviated to ELINT). Signals intelligence is a subset of intelligence collection management.
As sensitive information is often encrypted, signals intelligence in turn involves the use of cryptanalysis to decipher the messages. Traffic analysis—the study of who is signaling whom and in what quantity—is also used to derive information. WIKIPEDIA
Chinese intelligence would be unlikely to share intelligence about Helsinki with western intelligence agencies, although I suspect they were attempting to gather it.
However, it makes sense that British, French, German, and Dutch intelligence agencies were very active in Helsinki and have a wealth of information about what was communicated before and after the meeting. If Putin made a recording, which former intelligence official say is likely they would have hit the Mother (Russia) Lode if they intercepted that.
Even if they didn’t, knowledge of what Putin said or communicated to his associates, and what they said or communicated to each other after the meeting, would be invaluable.
Many American’s don't know that the Dutch have an excellent intelligence agency, the AIVD.
On January 25, 2018 Dutch newspaper de Volkskrant and TV program Nieuwsuur reported that in 2014 the General Intelligence and Security Service (AIVD) successfully infiltrated the computers of Cozy Bear and observed the hacking of the head office of the Democratic National Committee and subsequently The White House and were the first to alert the National Security Agency (NSA) about the cyber-intrusion. WIKIPEDIA
The United Kingdom, France, and Germany are considered to have intelligence agencies experts consider to be among the 10 best in the world. The most famous alumni of the UK’s MI-6 are James Bond and Christopher Steele. The General Directorate for External Security, the DGSE, is France’s external intelligence agency. Germany's external intelligence agency is called Federal Intelligence Service of Germany. It is often referred to as the BND, the abbreviation for its German name, Bundesnachrichtendienst.
If Trump was a normal president and allowed Americal officials in the meeting between the American and Russian presidents, American and allied intelligence agencies still would have been gathering Helsinki SIGINT.
Alarmingly, Trump being the opposite of a normal president, the only way American intelligence agencies may learn what was said between Trump and Putin is from our spy friends at the AIVD, MI-6, BND, and the DGSE.
What they know would go beyond what was actually said in the meeting. If we only knew the words said by Trump in that meeting we would know whether he was lying or whether he committed treason.
We may not ever need to hear those words if foreign intelligence agencies conveyed discussions between Putin and his associates to the CIA, FBI (and I think Mueller would have that) this could prove beyond a reasonable doubt (among reasonable people) that Trump lied and engaged in a conspiracy with Putin.