Barack Obama if I remember correctly.
So, yet another thing we can't pin directly on Donald Trump.
And it's also not a phenomenon that is limited to just the United States. Cas Mudde has a really great opinion piece in the Guardian about all this:
How and why did we get here? First and foremost, through a long process of cowardice, failures, and shortsighted opportunism of the mainstream right. Already in 2012, in the wake of the deadly terrorist attack on a Sikh temple in Wisconsin, by a longtime prominent neo-Nazi, I wrote, “the extremist rhetoric that comes from so-called law-abiding patriots should be taken more seriously”. I advised Republican leaders to “be more careful in choosing their company and insinuations”. What happened, however, was the opposite: far-right ideas and people were mainstreamed rather than ostracized.
As in so many other things, Donald Trump has been a major catalyst of this process, but not its initiator. The radicalization of the US right wing predates Trump by decades. It even predates the Tea party, which mostly helped to bring the far right into the heart of the Republican party. Obviously, racism and racist dog-whistling have been key to the party since they launched their infamous Southern Strategy in the 1970s, which brought white Southerners to the Republican party, but this goes far beyond that. The radicalization is not just ideological, it is anti-systemic.
I'm not sure if I would say that Trump was a "major catalyst", but he has definitely played and been associated with this trend. I am also not sure that I would put the blame solely on the right, since no one has called out this movement with any real force on either side. It's too easy to finger point than to address this issue.
On the other hand, it is long past time to have done anything about this issue. But what needs to be done is some serious self-examination by all sides as to WHY the situation is what it is. There are some very real issues raised by all this, but it's easier to play games than to address the flaws in the system.
A major flaw is that US elections are indeed not very democratic from a two party system that shuts out other players, to gerrymandered districts, not directly electing the president, among a long list of problems screaming for reform. These problems are internal and not caused by foreign nationals.
The writing was on the wall long before Trump and may bring someone far worse than Trump unless the problems are addressed.