The FBI and CIA are always at work. Part of that work is keeping track of enemy agents. Part of that work is surveillance, including wire-tapping. While monitoring known Russian agents, the name "Carter Page" came up. He was aiding the Russian agents. As a result of Page's hidden involvement, the intelligence community began surveilling Carter Page as an unannounced foreign agent.
Any U.S. citizen may register as a lawful Foreign Agent. If you want to middleman-broker some across-national-borders deal, say the sale of grain, you are acting as a foreign agent. You register your intent and all is above board.
However, failure to disclose is a crime and that is collusion.
Colluding with foreign interests leaves the colluding party open to foreign manipulation because of its criminality, especially when involved with sworn enemies such as the Russians.
"Collusion" is defined as a secret or illegal cooperation or conspiracy, especially in order to cheat or deceive others. If you do not disclose, you have criminally deceived: it is simple and straightforward collusion.
It was this Russian/Page collusion that was revealed to the new President Trump, many months after the FBI had started their surveillance to protect America against the Soviets.
In order to keep this fruitful surveillance going, U.S. law demands an accounting of its continued need, so every 90 days, it must cease or be recertified by a FISA appointed federal judge.
The individual in our government charged with that task has been the deputy attorney general. In the Obama administration, this position was held by Sally Yates.
Every 90 days ever since the start of FBI surveillance, the FISA Court reexamined the evidence against Russian foreign agent Carter Page and duly renewed the extension. When the choice of the current administration, Rod Rosenstein, took over, he continued that application as ordered by law.
Please note three things: this FISA review is the job of the judiciary, not the executive branch; all of this cloak-and-dagger stuff started long before the current president took office; and Christopher Steele's later, entirely separate, investigation had no role in the FISA reviews of the collusion of Carter Page.
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