Transcript for Why a special counsel is investigating the Trump campaign's ties to Russia

So there's this special counsel investigating Russian interference in the 2016. Election and that's a big deal. Because special counsels or special prosecutors as it used to be called don't get appointed area office. Self how did he get here. Let's go back to may fourth. House Republicans pushed through their health care bill their first big legislative win under president dropped. And he is riding act like big smiled back flaps in the Rose Garden but that high doesn't last long. On May eighth Sally gates testified that asking January when she was acting attorney general she went to the white house with concerns about their national security advisor general Michael plant. Now fleeing you'll remember what an early drowned after he even got a prime speaking slot at the Republican National Convention. Where he led the crowd in the lock her up and that's right. Linked with in the inner circle. With his wife Sally Yates felt the need to flatten the White House about their old high. You see he lied to them about his contact with Russian officials specifically called a surrogate Wesley the Russian ambassador to the US. It would they reportedly talked about sanction. Back in December. Before trump with inaugurate while Obama with still president. Not only is that bad form undermining the sitting president backdoor talk. But it's possibly illegal remember Obama was pushing sanctions against Russia as punishment for interfering in the twenty election. If Clinton as an unauthorized fitted in with interfering in a dispute with a foreign government and you might have broken the law. But back to may. Gates warned the White House. Fleeing could be blocking the Russians would know about that call and it looks like the White House got the vice president was actually out defending Flynn there was no contact. The trump doesn't force that went for another eighteen days instead he fired gates for not defending traveled. The day after Yates is testimony on May ninth trump fires that BI director James coney in a letter. This is the man leading the investigation into the trunk campaign's ties to Russia. An Indian firing letter how includes an oddly specific line thinking Komi for assuring the president three times that he wasn't under investigation. At some ankle he hasn't there. But the stories explaining why he fired Kobe don't die. Questions pile up. Pressure built. And then the unraveling began. On May eleventh the New York Times reports trump demanded loyalty from Komi during a private meeting in January but police would give us the White House tonight. On May twelfth from tweets and veiled threat to coney they eat better hope there are no tapes of their conversations. On May sixteenth another bomb report trump disclosed classified information to Russian officials during their White House visit which by the way he can legally do. But given the questions about his ties to Russia Italy Rea has more on May sixteenth we learn that Komi takes note. Lots of from all his meetings and calls with child and he wrote a memo about one in particular in which the president asked him to stop the federal investigation into Michael planes. Saying quote I hope you can see your way clear to letting this go to letting lingo. That meeting took plea the day after flagrant. On May seventeenth the Department of Justice announces former FBI director Robert Mueller has been appointed as special counsel. With his own budget his own routines and all the power of the US attorney's smaller school is trot once and for all to get answers to these questions. The two weeks leading up to that felt like two years but remember that this special counsel's investigation. It only gaps between.

This transcript has been automatically generated and may not be 100% accurate.