'Start Here': Sanders and Warren tensions simmer ahead of debate and Astros fire manager, GM after cheating investigation

Here's what you need to know to start your day.

It's Tuesday, Jan. 14, 2019. Let's start here.

1. Progressives and punditry

Democratic presidential hopefuls will face off on the debate stage today for the last time before the Iowa caucuses amid increasing tensions between Sen. Bernie Sanders, I-Vt., and Sen. Elizabeth Warren, D-Mass.

Warren confirmed a CNN report on Monday that in 2018, Sanders disagreed with her when she said a woman could win in 2020 against President Donald Trump, but she added, "I have no interest in discussing this private meeting any further because Bernie and I have far more in common than our differences on punditry."

Sanders denied ever telling her that a woman couldn't win, saying in a statement, "It’s sad that, three weeks before the Iowa caucus and a year after that private conversation, staff who weren’t in the room are lying about what happened."

On today's "Start Here," ABC News' Adam Kelsey breaks down the drama between the progressive pair, who had maintained a non-aggression pact at the beginning of the campaign: "If there's any time for these two to create some separation between each other it's going to be at this debate tonight."

2. Trainees kicked out

Attorney General William Barr announced Monday that 21 Saudi students will be expelled from the U.S. following an investigation into last month’s deadly shooting at the Naval Air Station in Pensacola, Florida.

Barr said the shooter, Lt. Mohammed Alshamrani, was "motivated by jihadist ideology."

ABC News Chief Justice correspondent Pierre Thomas says that while the 21 military trainees did not aid in the attack, some were found to have "derogatory material" on their electronic devices.

3. The two popes

In a new book, retired Pope Benedict XVI is speaking out against allowing married older, married men to be ordained as priests, a proposal that Pope Francis is considering to address a priest shortage.

"I think it raises the question of how do you deal with two Catholic leaders being alive at the same time," says ABC News' Megan Williams in Rome. "Many Catholics are saying, is this the time where we should start bringing in rules to deal with popes who more and more will retire instead of die."

4. Two out in Houston

The Houson Astros fired general manager Jeff Luhnow and manager A.J. Hinch on Monday, hours after MLB handed down a one-year suspension for the pair in connection with a sign-stealing scheme during the 2017 season.

According to the investigation’s findings, which was initiated after a 2019 article by The Athletic, the Astros utilized footage from the center field camera to identify signs and used a "runner" to relay the information to the dugout.

In separate statements, both Luhnow and Hinch denied having any role in directing or overseeing the scheme but acknowledged they failed to stop the cheating.

ESPN's Jeff Passan tells "Start Here" that the investigation was recently expanded beyond the Astros: "What makes this thing so tricky for Major League Baseball is it wasn't just the Houston Astros who were using technology to make themselves better."

"Start Here," ABC News' flagship podcast, offers a straightforward look at the day's top stories in 20 minutes. Listen for free every weekday on Apple Podcasts, Google Podcasts, iHeartRadio, Spotify, Stitcher, TuneIn or the ABC News app. Follow @StartHereABC on Twitter, Facebook and Instagram for exclusive content and show updates.

Elsewhere:

'A nightmare': A 22-year-old man has been arrested after pushing his elderly landlord so violently down the front stairs of his building in a dispute over rent that the man died.

'No one did anything': Authorities dropped charges against an Alabama man who was accused of killing his wife 30 years ago, saying another man has confessed to the murder.

'No threat to aviation': A missing teen with autism was found at Orlando International Airport on Friday after passing through a Transportation Safety Administration checkpoint by using someone else's boarding pass, authorities confirmed.

'More charges are expected': A man born before World War II even began has been arrested after allegedly robbing a bank in South Carolina while wearing a mask.

From our friends at FiveThirtyEight:

'Why Booker’s campaign never really took off': On Monday, New Jersey Sen. Cory Booker dropped out of the presidential race. And for a candidate who has long been pegged as a presidential aspirant, even while he was still mayor of Newark, it’s remarkable how little impact Booker’s candidacy made on the Democratic primary.

Doff your cap:

A Granbury, Texas, man who bravely jumped into action last month by gunning down an active shooter at a church has received the state's highest civilian honor.

Texas Gov. Greg Abbott presented Jack Wilson with the Medal of Courage Monday morning for stopping "a gunman in a deadly shooting at a church in North Texas."

Wilson, 71, is a former reserve deputy sheriff who was at the West Freeway Church of Christ in Fort Worth on Dec. 29, when Keith Thomas Kinnunen opened fire during a service.

"I don't see myself as a hero," Wilson told reporters after the shooting. "I see myself as doing what needed to be done to take out the evil threat."