In a year when the president fought with congressional leaders on live TV and celebrities set off mental health scares on Instagram, it's hard to believe there'd be much mystery left behind the news. But not everything played out in front of our eyes.

As 2018 comes to an end, some stories that made the biggest headlines and drew the greatest scrutiny leave open questions. Here's a look at some of the things we still don't know:

Who in the Trump administration wrote the anonymous "resistance" op-ed?

A single article became a Beltway obsession for a few days in September: A New York Times op-ed by an anonymous senior official in President's Trump administration who claimed to be part of the "resistance" that was "working diligently from within to frustrate parts of his agenda and his worst inclinations." The author described efforts by a group of administration officials to curtail some of the president's rasher actions, and assured Americans "that there are adults in the room."

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Readers online picked apart word choices and the subtlest turns of phrase to try to figure out who wrote it. Was it Vice President Pence, who has a thing for using one of the article's most distinctive words, "lodestar"? Was it one of the Cabinet members who criticized Trump during the 2016 campaign, like Nikki Haley? Was it someone behind the scenes that we hadn't even heard of? Whoever it was, the author kept their anonymity intact, and could still be working in the Trump administration today.

Who won the $1.5 billion Mega Millions jackpot?

One of 2018's luckiest people remains nameless. By late October, the Mega Millions jackpot soared to $1.5 billion, the second-highest lottery drawing in U.S. history. And then a convenience store in Simpsonville, South Carolina — population 22,000 — sold the winning ticket.

To this day, we don't know who bought it or if the winner even claimed the cash. And we may never find out, since South Carolina is among the few states that allow lottery winners to remain anonymous.

Does a racist Trump tape actually exist?



Rumors about secret recordings of Donald Trump using the N-word on "The Apprentice" set surfaced during the 2016 campaign. But those supposed tapes became a bigger story in 2018 as two celebrities suggested they might emerge soon.

Actor Tom Arnold devoted an entire eight-episode Viceland series to hunting for the Trump tapes. The show ended with him empty-handed.

Meanwhile, former "Apprentice" star and White House official Omarosa Manigault-Newman started releasing recordings she'd secretly made on the job as she promoted her memoir, "Unhinged." One recording, obtained by CBS News, captured Trump campaign aides discussing the alleged N-word tape and how to respond if it became public. Omarosa claimed that whoever had the tape was going to release it around the midterms. But the elections came and went, and the tape — if there is one — never came out.

All along, Mr. Trump has denied ever using the slur, tweeting in August that "I don't have that word in my vocabulary."

What's causing a mysterious "polio-like" illness in kids?



A troubling illness spread fear across America this year: acute flaccid myelitis (AFM), a disease in the nervous system that can cause paralysis, mostly affecting children. The outbreak drew comparisons to the poliovirus, which the U.S. eliminated with vaccines decades ago. The CDC said there were 165 confirmed cases in 36 states this year — a sharp increase from 35 confirmed cases in 16 states in 2017. More than 90 percent of the cases were in children.

But despite the widespread attention to the outbreak, there's still little understanding of the illness. "This is truly a mystery disease," a top CDC official told CBS News, though scientists are working hard to unravel it. The CDC said it doesn't know what causes most AFM cases, and there is no specific treatment for the illness. Fortunately, it doesn't appear to be transmissible from human to human.

The agency's suggested prevention methods include washing your hands and avoiding mosquito bites, to reduce the risk of viral infections that could lead to AFM. And get the polio vaccine to protect against that dreaded virus, though the CDC noted that no AFM patients in the U.S. tested positive for polio.