In fact it is true. Even the liberal media outlets openly acknowledge this is the case, they're not hiding their bias in any manner, they're openly "resisting." The well-known Pew study in the first year of his administration showed that the negative media coverage was 3x that vs the Obama Admin. The positive coverage was 1/5 that of what the Obama Admin saw. It has only gotten worse since then.
"News Coverage Of Trump More Negative Than For Other Presidents"
https://www.npr.org/2017/10/02/555092743/study-news-coverage...
MSNBC, CBS News, NBC News, ABC News, CNN, NY Times, Washington Post, Bloomberg, NPR, all talk-show hosts, nearly all journalists (roughly 9 out of 10 vote Democrat to begin with), nearly all celebrities, essentially all of Hollywood - these groups are all as close to universally against Trump as you can get. It's not subtle, it's nearly all-encompassing. Estimating that 90% of media is stacked against the Trump Administration is an understatement.