Adam Goldman, one of the reporters who broke the story, commented that “this was a lawfully predicated investigation. And my understanding was that the people involved understood the gravity of it and knew they would have to answer for it someday, when Congress conducted oversight… The people who do this kind of work are not fools and know it will become public, just like the Carter Page FISA application became public.”
The New Yorker

According to a former FBI agent, “the bureau would have had to possess strong evidence that Trump posed a national security threat to meet the threshold for opening such an investigation. But the more important question now is not how or why the case was opened, but whether it was ever closed…

“If the counterintelligence case against the president was eventually closed because it found that Trump did not pose a threat to U.S. national security, Trump should welcome Mueller’s report reaching Congress. This conclusion would stop the speculation about Trump’s relationship with Russia… But if it wasn’t, and the threat to national security is ongoing, then informing Congress of the nature of the threat is paramount.”
Washington Post

According to former FBI General Counsel James Baker, “to the extent that firing Comey was the result of a decision to shut down the investigation… that would frustrate the FBI’s ability to ascertain what the Russians and their confederates had done. In other words, ‘not only would it be an issue about obstructing an investigation, but the obstruction itself would hurt our ability to figure out what the Russians had done, and that is what would be the threat to national security.’”
Lawfare Blog

“Trumpism is a godsend to Putin and a nightmare for governments in his sights—including Trump’s. The U.S. commander-in-chief is out of sync with his own administration, not to mention the government as a whole. Note his stubborn yearning to lift sanctions on Putin’s pet oligarchs… We don’t need news reports to tell us that Trump is giving Putin what he wants.”
Politico

Regarding Manafort, “we don’t yet know how [Manafort’s] data was used by Russian agents, if at all. But polling information could have been extremely useful in targeting illicit social media campaigns and other political activities in the most effective way… this is potentially the most concrete evidence to date of coordination between the Trump campaign and Russians.”
Washington Post