"Our lawyers at the Department of Justice say we have the legal authority to do this," Johnson said in a speech about the nation's immigration system at Rice University in Houston. He added that the president's actions, known as deferred action, are "the right thing to do...Over and over again, in the life of this nation, there have been classes of people who, by virtue of their race, gender, religion, or nationality, exist on the margins of society and struggle to seek our acceptance."

"It has been the tradition of this great nation that, ultimately, we hear their claims and grant them relief," Johnson said.

In his remarks, the secretary also criticized what he called the "emotion and partisanship wrapped around the subject of immigration. Facts are too often drowned out by demagoguery, suspicion, exaggeration, and misperception."

As an example, Johnson cited a 2013 public opinion survey in which Americans were asked whether the number of immigrants entering the country illegally is higher or lower compared to 2003. A majority, 55 percent, said illegal immigration was rising.

In fact, Johnson said, "the opposite is true," pointing to indications that illegal immigration flows are far lower than in the past. Evidence has been emerging that such flows have fallen to their lowest level in at least two decades, with DHS and some experts crediting the billions of dollars the nation has poured into southwest border security. Other experts point to other factors for the change, such as demographic changes and economic improvements in Mexico.

"I am on a mission to separate fact from fiction about immigration in the public mind," and share more information," said Johnson, who acknowledged that DHS has said too little publicly about the subject in past years. "This too breeds suspicion and misperception to fill the void," he said.