Character Analysis
Less of a character and more of a symbol, Austin Stoneman represents the Radical Republicans, a group of politicians who advocated for harsh punishments against the South in the aftermath of the Civil War. While there are many valid arguments for this approach, D.W. Griffith clearly thinks that these guys were power-hungry, carpetbagging chumps.
Absolute Power...
The film emphasizes Stoneman's power-drunk nature from the moment we meet him. One subtle moment is when we see him awkwardly adjust his wig while speaking with another politician, which is a clever way of making him look phony and buffoonish. The real power grab begins after President Lincoln is assassinated, however, making Stoneman the "uncrowned king" of Washington.
From there, Stoneman enacts a range of policies that seem totally justifiable by modern standards, but downright horrifying to poor old oppressed D.W. Griffith—namely, "full equality" between black and white people. Gasp.
While this is obviously a good thing from our perspective, Griffith sees this as a Trojan Horse for Stoneman to force his Northern values on the South.
Chipping Away at the Stone
More than that, however, Griffith is intent on portraying Stoneman as a hypocrite. A key moment occurs near the end of the film when Silas Young, Stoneman's biracial protégé, tells him that he wants to marry a white woman. Stoneman is gung-ho until Lynch reveals that he's talking about Elsie, Stoneman's daughter.
He freaks.
This might be the one moment when Griffith portrays racism in a real way. There are plenty of people out there who are supportive of racial equality in theory, but have no interest in placing it in practice in their actual lives. That's a big disconnect. One insightful moment doesn't make up for the film's rampant historical revisionism, of course, but it adds a bit of nuance to an otherwise ridiculous character.