Now artists and politics are notorious for not mixing well. Two great examples of that would be David and Hitler. While artists should never give up their day job for politics, they historically can be successful involving themselves minimally in politics. Of course I am specifically thinking of Gainsborough and Reynolds when I say this.
The two artists were notorious rivals and actually quite opposite of each other. Gainsborough was rather reserved and tended to side with King George on political issues, therefore he was associated with the Tories. On the opposite spectrum was Reynolds, who was more outspoken and bold. He was the head of the Royal Academy and therefore left King George no choice to name him as the royal painter. Reynolds' political views tended to be more liberal and his friends tended to be Whigs, creating a further polarity between him and the quiet Gainsborough. The royal family actually always preferred Gainsborough, and continued to commission works from him even after naming Reynolds the royal painter.
I find that comparing both artists' depictions of their politician counterparts produces some interesting results. Charles James Fox and William Pitt the Younger were political rivals just as Gainsborough and Reynolds were artistic ones. Judging from their portraits, the individual artists' aesthetic styles aren't the only things separating the sitters. Fox's girth strongly contrasts with Pitt's narrow frame. Fox sloppily wears blue while Pitt favors a neat black. Reynold's cakey application of paint accurately displays the psychological boldness of Fox. The wispy strands that distinguish Gainsborough's strokes meet in a cohesive and neat form to display Pitt, who devoted himself to peacing together a neat infrastructure of government out of the surrounding chaos. The amazing contemporary artist, Julie Heffernan theorizes that every painting an artist creates is a self-portrait because it shows the artist; these examples make truth of her statement.
Despite being rivals, both artists remained successful. Aristocrats such as Georgiana were rich enough to be painted multiple times by both artists. I think Reynolds' esteem and general fondness for her shines through in his images of her in comparison to Gainsborough's, which seem seem to falter usually for him. However I should note that Gainsborough did throw down his brush in frustration upon his dissatisfaction of being able to portray her likeness. Ah, the price of perfection!
Left: Gainsborough, 1783 Right: Reynolds, 1776