One of the things that is important to note about Twain and his views on politics and culture of the United States is that many people felt he got deeper into the heart of things than many of his peers and thats why his opinion was so valuable. William Dean Howells, the editor of The Atlantic Monthly described him as follows
It is in vain that I try to give a notion of the intensity with which he [Mark Twain] pierced to the heart of life, and the breadth of vision with which he compassed the whole world. ... Emerson, Longfellow, Lowell, Holmes—I knew them all and all the rest of our sages, poets, seers, critics, humorists; they were like one another and like other literary men, but Clemens was sole, incomparable, the Lincoln of our literature.
In terms of his view of politics, in "The Edge" he wrote:
The political and commercial morals of the United States are not merely food for laughter, they are an entire banquet.
He often was very cynical about the way that the government operated and about most people in positions of power.
He was pretty positive about the potential of Americans and the early direction of the country but had grown somewhat cynical as evidenced by the following quote from a speech he gave in 1890:
We are called the nation of inventors. And we are. We could still claim that title and wear its loftiest honors if we had stopped with the first thing we ever invented, which was human liberty.
If you read his novels and his short stories, he clearly has a belief in the goodness of the human character and the ability of people to be good and to make good decisions and care for each other, but he is also more than happy to point out their flaws and the fact that often the most celebrated and famous cannot stand up to the actions of the good and downtrodden people of the world and of the worlds of his stories.