I think Trump is a large reason why the Democrat party has moved so far to the left. There are positions today taken by mainstream Democrats that would be considered radical even for fringe groups ten or twenty years ago.
I'm not sure. I think they are both symptoms of the same underlying issue. The centrist consensus of the last few decades resulted in mainstream political parties being almost indistinguishable from one another. This led to a widespread feeling of disenfranchisement amongst the general public, millions of people who felt that no-one represented them, and that it didn't matter which party won, the result for their own everyday lives was always the same.
There are people to the right of centre who feel unrepresented, and people to the left of centre who feel exactly the same. The rise in the US of politicians such as Trump and Sanders is mirrored in other nations. Here in the UK, we had Jeremy Corbyn on the left, branded an extremist by his own party, and the pro-Brexit faction on the right, previously extremists within their own party, but now running the country.