What does "it" of "it also warranted a counterintelligence" refer to?
Muller's investigation "also warranted a counterintelligence"??

Context>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Comey’s firing was obviously the tipping point. Investigators reportedly shed their previous reservations about the inquiry after Trump’s televised admission to NBC News’s Lester Holt that the Russia investigation was on his mind when he did it. Another red flag was Trump’s attempts to include a reference to the Russia investigation in Deputy Attorney General Rod J. Rosenstein’s letter justifying the firing.

We already know that these few days comprised a central event in Mueller’s investigation into whether Trump obstructed justice, but the idea that it also warranted a counterintelligence inquiry is notable. It’s one thing to deliberately hamper the investigation; it’s another to suspect Trump might have done so on behalf of Russia. And were this to ever lead to any concrete conclusions, that the Holt interview will apparently have been an extraordinary misstep by Trump, who has often seemed to blurt out unhelpful statements about his true motivations.