I don't think anyone thinks the Russians literally "hacked" the election as in broke into voting machines and put it bogus votes or the like.

What it is clear that what the Russians did do is spew non-stop anti-Hillary fake news propaganda onto Facebook and other social sites that immediately got picked up and amplified by Breitbart and Fox.

It is also pretty clear that the Russians broke into Hillary's email server and dumped the results into the Internet so that Breitbart and the other idiots could comb through it looking for things to take out of context. Trump and Fox made claims that they found evidence of corruption in the emails but never provided a smoking gun. But that didn't keep it off the front pages

Basically the Russians were acting as Trump's dirty tricks squad. Which would be legal if they were US citizens but election law specifically forbids candidates from getting help of any kind from foreign sources.

As for Trump's involvement, he went on national TV and begged the Russians to commit crimes (hack Hillary' server) to help his campaign. He can't exactly act surprised if they took him up on it.

The current investigation is trying to find out exactly how criminal the Trump campaign was, but he is on tape committing treason by engaging an enemy power to help him get into office.

He also is on video admitting that he fired Comey because he wouldn't back away from the Flynn investigation. That's obstruction of justice.... a felony.

Now Don Jr. has confessed on camera to meeting with Russian agents to get opposition data against Hillary... also a violation of election law.

I don't think collusion is quite the right word, it's more like getting illegal political favors from your foreign business contacts who just happen to be "ex" KGB and/or Russian mafia.

So Yeah, it isn't exactly a secret.