"Frank Langella and Michael Sheen do not attempt to mimic their characters, but to embody them. There's the usual settling-in period, common to all biopics about people we're familiar with, when we're comparing the real to the performance. Then that fades out and we become absorbed in the drama."
Go see it.
*Disclaimer: Bear in mind, of course, that I was born twelve years after the Watergate scandal broke, so my ability to judge the accuracy of Langella's impression may be somewhat hampered. However, my ability to judge a good performance is not, and this was a very good performance, with an even better one by Michael Sheen.