The first instinct is to circle the wagons and deny there is an issue. The British and Americans (with the help of Poles) read German military code all throughout WWII, and the German intelligence officials refused to believe they had a problem.
The German Navy suspected there was an issue and modified their code machines, and it worked for a while, but was not successful for very long once the Allies figured out what they had done. It was a disaster of epic proportions for the Germans, and looking back the blind acceptance of hundreds of ‘coincidences’ seems stupid beyond belief.
But, the failures continue even today.
I watched a TV show recently that told of a Brit who was fundamental in code breaking after the Enigma was captured.
He developed a technique called Traffic Analysis to place all the radio signals in context and derive intelligence there from. His work remained secret for a long time, even after the divulgence of the enigma posession. The technique is fundamental to the intelligence business today. It is still oficially secret.
Obama being commander in chief commanded the resources and tecnique to be used against his domestic enemies, namely Donald Trump. We have not yet leaned of the others that we can be certain who were surveiled...... all of the Republican candidates at a minimum