Most American automobiles are powered by internal combustion engines: Gas or diesel goes in, tiny explosions power pistons and turn a crankshaft, the car moves forward, and carbon dioxide goes out.

But a growing chorus environmental activists, business analysts and auto executives are predicting a sea change as battery-powered electric vehicles grow in popularity.

Before President Trump even uttered the words "national emergency" on Friday, there was already a lot of talk about legal challenges.

Here's the central question: Is it constitutional for the president to ignore Congress' decision not to give him all the money he wants for a Southern border wall — and, instead, get it through a declaration of a national emergency?

You're reading NPR's weekly roundup of education news.

An end to the Denver teacher strike

Denver teachers returned to the classroom this week after the Denver Classroom Teachers Association and Denver Public Schools reached a tentative labor agreement Thursday morning. Teachers in Denver had been on strike since Monday.

Updated at 11:53 p.m. ET

A man armed with a handgun entered the Henry Pratt Co. in Aurora, Ill., on Friday afternoon and killed five civilians, officials announced at a news conference. Five police officers were also wounded.

When you talk to Virginia Democrats these days, you hear a lot of words like "disappointing" and "frustrating."

That's because the men at the top of state government — and at the center of these scandals — have been well-liked by a lot of people who worked hard to help elect them.

"It really is kind of a hard thing to reckon with — some of your heroes either causing embarrassment or shame or disappointment or anger," said Alexsis Rodgers, president of Virginia Young Democrats.

The Department of Homeland Security has announced new guidelines to track child marriages among immigrants in the United States.

While debates on immigration have focused on national security, and President Trump's determination to build a wall along the southern border has resulted in a national emergency declaration, the new rules address a far lesser known immigration issue.

Under the Immigration and Nationality Act, there is no minimum age requirement for a person to request or benefit from visa applications in which spouses or fiancées are minors.

The Senate Finance Committee is launching a bipartisan investigation into how a conservative think tank aided Maria Butina, the admitted Russian agent who sought political influence through her ties with the National Rifle Association.

Butina pleaded guilty to acting as a foreign agent in the United States in December, and her alleged Russian government handler, Alexander Torshin, was sanctioned by the U.S. in April 2018.

A federal judge imposed a gag order on Friday in the case of Republican political consultant Roger Stone.

Judge Amy Berman Jackson ordered that lawyers and others in the case must not talk about it publicly in ways that "pose a substantial likelihood of material prejudice" and specifically they must not use the area outside court in Washington, D.C., as a venue for those kinds of statements.