Bernie Sanders, like Donald Trump, says he's "angry" – and voters seem to be angry, too. (Peter Stevenson/The Washington Post)

We already knew Donald Trump was angry. It’s hard not to notice. But he’s not the only presidential candidate raging against the system.

Bernie Sanders has always seemed a bit grumpy, even frustrated, in his attacks on the American political system. And now he’s embracing what Trump has called “the mantle of anger.”

“I am angry,” Sanders said on CBS “Face the Nation” Sunday, in a manner reminiscent of Trump’s assertion at the Fox Business Network GOP debate on Jan. 14. “The American people are angry.”

Sanders was responding to accusations by former president Bill Clinton that he seemed too frustrated on the campaign trail. The line has since become a part of Sanders's stump speech, in which he goes on to list the various ways people are angry (although there are, obviously, big differences between Sanders and Trump in terms of the objects of said anger). Sanders’s anger, he says, is directed at economic problems, the American political system, student loan debt, Wall Street, and you guessed it – “the billionaire class.”

Both Sanders and Trump have had a lot of success, at least in polls leading up to early primary votes, tapping into that frustration. Their rallies are noticeably more raucous than those of their rivals -- and their crowds often larger.

That voter frustration is reflected in polls. A Monmouth University poll released Monday asked adults in the United States, "How many Americans do you think feel angry about Washington politics?" Sixty-two percent said “most” or “all” Americans are angry about politics.

It should come as no surprise, then, that the two candidates who are “angriest” about the U.S. political system are currently leading in both Iowa and New Hampshire, according to the latest Real Clear Politics poll averages. Both candidates have single-digit leads in Iowa and double-digit leads in New Hampshire, as of Monday.

Of course, Sanders and Trump are both polarizing candidates in their respective parties. Both Republican and Democratic party leaders are wary of the possibility of outsider candidates winning their party’s presidential nomination, afraid that they will prove inaccessible to moderate voters.

But right now, the angry voices are the loudest ones in the room.