Americans knew almost nothing about the Mueller investigation until it was completed and the report was released. On the day after Mueller testified before Congress, Trump phoned Volodymyr Zelensky seeking political help. There were other people in the room and/or on the line when Trump made the call. Yes, witnesses. Mueller was unable to prove, or disprove, that Trump was guilty of obstruction of justice. The phone call is different. We all know Trump made the call, we know he withheld military aid then asked for a "favor" and we know he wanted foreign agents to dig up dirt on the man he could be running against in 2020. Trump, surprisingly, admitted all this.
The Mueller report probably didn't lead many people to think Trump should be impeached. Trump's solicitation of foreign interference in a US election, well, that's pretty clear-cut. It's a violation of his oath of office, it jeopardizes the fairness of a Presidential election and it poses a threat to national security. The number of Americans who believe Trump should be impeached is growing. Trump is already using the threat of impeachment as an issue in his campaign ads: "Don't let those angry, bitter, evil Democrats steal the election!" (I'm paraphrasing.) Trump's blindly loyal supporters – his "base" – will continue to worship him and defend him no matter what happens. A growing number of the rest of us want him impeached and removed from office before he can do further damage to our democracy.