One of the most widely used drugs in the world isn't really a drug, at least not in the usual sense.

It's more like a dye.

Physicians call this drug "contrast," shorthand for contrast agent.

Contrast agents are chemical compounds that doctors use to improve the quality of an imaging test. In the emergency room, where I work, contrast is most commonly given intravenously during a CT scan.

As Democratic presidential hopefuls seek to grow the small-donor juggernaut that fueled the party's takeover of the House of Representatives last year, the Democratic National Committee is giving them a firm shove, offering slots in the presidential primary debates to candidates who build a broad fundraising base.

"I really believe that we're at our best when we're connecting with people," DNC chair Tom Perez told MSNBC recently. "That's how we won in 2018, and frankly that's how Barack Obama won in 2008. And that's exactly what I think this will incentivize."

Updated at 4:58 p.m. ET

After nearly two years of waiting, special counsel Robert Mueller's report into Russia's attack on the 2016 presidential election is finally done. And there's growing bipartisan pressure on Attorney General William Barr to make it public.

Robert Mueller may have completed his report, but other investigations into President Trump are expected to carry on for months.

There are, broadly, two kinds: those being undertaken from within the executive branch and those being run by members of Congress — mostly Democrats in control of major committees in the House.

A jury in Pennsylvania has acquitted a white former police officer who fatally shot an unarmed black teenager in the back, setting off a series of angry protests.

Michael Rosfeld was a rookie officer with the East Pittsburgh Police Department who had been sworn in just hours before shooting 17-year-old Antwon Rose II last June. Rosfeld was charged with murder.

The stock market tumbled Friday as investors digested an ominous warning sign: Interest rates on long-term government debt fell below the rate on short-term bills. That's often a signal that a recession is on the horizon.

The Dow Jones Industrial Average fell more than 460 points Friday, or about 1.8 percent. The broader S&P 500 index fell 1.9 percent.

Ordinarily, the yield on long-term debt is higher, just as 10-year certificates of deposit tend to pay higher interest rates than three-month CDs.

A fire at a petrochemical plant outside of Houston briefly reignited Friday, sending up another plume of black smoke at a site where a blaze had erupted earlier this week. The fire was preceded by a chemical spill into the Houston Ship Channel.

Faith-based adoption agencies in Michigan that benefit from taxpayer funding will no longer be allowed to legally turn away same-sex couples or LGBTQ individuals based on religious objection, under the terms of a settlement in a lawsuit alleging the practice constituted discrimination.