"Steves's core motivation is hope and optimism. It's what gave him the strength to get up each time he was beat before he was turned into the Captain. He has to believe that good will overcome evil... that right is stronger than might."
What's interesting though is that Steve isn't Captain America anymore- at least not in the comics. The shield has been passed to Sam Wilson, and while both characters are committed to the same core values (freedom, equality, truth, and justice), the characters are currently at odds over how to embody those values.
Who was he before?
Captain America has always been a symbol of more radical ideals. He's a patriotic symbol yes- but he's no jingoist pro-America zealot. The character has been at odds with 'traditional' values many times. He was created by two Jewish-Americans months before the United States entered World War II, when plenty of Americans were more than comfortable with letting Hitler commit atrocious crimes. Creating a character to combat the Nazis in the name of American patriotism was incredibly subversive. And that isn't about to change.
There's only one thing that sets Steve and Sam apart.
And trust matters.
Steve Rogers has always been characterizes as having a superheroic amount of hope. That's not something the serum gave him. Even when he was small and sick, he always believed that standing up for the right thing was worthwhile because he had faith that he wouldn't be alone.
"Steve Rogers, in his heart, BELIEVES that when the chips are down, when its values are at stake- his country will do what's right. And me? In my heart? I can only hope it will." -Sam Wilson
And while Sam's hope is beautiful- his skepticism is also important. He's not just a hero in a star-spangled costume. He's also a black man living in America. The same country where 547 people have been killed by police as of this past June (black people are being killed at more than twice the rate of white and Hispanic people- via the Guardian). So while yes, we should always hope that people will do the right thing, the trust has been broken in a big way.
So yes, Captain America's values have changed.
They changed because they had to. Because all the hope in the world isn't enough anymore. Because right now trust is something that needs to be earned. And in the meantime, there's work that needs to be done. Protecting immigrants at the border from violent vigilantes? That's Captain America through and through, business as usual. But protecting informants, because it seems like they might not get a fair trial? That's a shade of grey that the hero hasn't had to live in before. And maybe that's the Captain America we need right now.