The Obama part was a bit of hyperbole, not a strawman. But people really were saying Trump is literally Hitler. http://www.huffingtonpost.com/entry/the-road-ahead_us_57e03b...
And it's not a mainstream perspective, it is at best a hyperbole of people saying hyperbolic things.
Two hyperboles don't make a right.
2. https://www.salon.com/2016/12/20/14-signs-show-trumps-politi...
3. https://newrepublic.com/minutes/124205/yes-donald-trump-fasc...
4. http://www.aljazeera.com/indepth/features/2016/11/foul-stenc...
5. http://www.forbes.com/forbes/welcome/?toURL=http://www.forbe...
6. https://www.theatlantic.com/politics/archive/2016/08/america...
2. No mention of Hitler. A point by point comparison to a historical and previous description of fascism.
3. Not Hitler, talks about conservatism and totalitarianism.
4. No mention of Hitler anywhere.
5. " I am not suggesting that what is happening in the United States replicates in every sense what happened in Italy and Germany. "
6. "The Republican presidential candidate is not a Fascist, but his campaign bears notable similarities to the reign of Italian dictator Benito Mussolini."
Compare these viewpoints to the claim of "But people really were saying Trump is literally Hitler."
Edit: I should also say that I don't doubt you could come up with something somewhere where somebody claimed that Trump is "literally Hitler." However, it is not a prevalent or even mainstream viewpoint. Even calling Trump a fascist, and defending it based on evidence, is a pretty extreme and rare viewpoint.
"How do you talk people down after spending a year telling them Hitler was coming to power?" vs. "How do you talk people down after spending a year telling them a fascist was coming to power?" isn't a very meaningful distinction to me in that context. Your mileage may vary. Many mainstream outlets have expressed that opinion for a long time, and it's a point of view I've seen defended here on HN many times in political threads. I don't think it's a fringe viewpoint at all.
The "literally Hitler" smear is an attempt to distinguish that careful, and important distinction, so that the entire thought can be dismissed as ridiculous.
Looking at each of those articles where they say "not hitler, but he still is making noises like he'll be bad," do you think that needs to be walked back? Were they ignoring reality, or facing an unpleasant reality?
"Literally Hitler" is not a thoughtful, fair, or even useful characterization of these viewpoints.