This morning we're tracking news of a mass shooting at a Southern California bar overnight. Officials say at least 12 people were killed, including a law enforcement officer, after a lone gunman opened fire in the western themed bar in Thousand Oaks. The gunman also is dead. This is still a developing story and you can check Philly.com throughout the day for updates.

Take care of yourselves and each other today, folks.

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— Aubrey Nagle (@aubsn, morningnewsletter@philly.com)

» READ MORE: California bar mass shooting: The latest

A gunman opened fire at the Borderline Bar and Grill in Thousand Oaks, California Wednesday night killing at least 12 people, including a sheriff's deputy responding to 911 calls about the shooting. The gunman was found dead inside the bar.A dozen others are also reported wounded. Reports say the country dance bar was packed with hundreds of people for "college night."

The gunman has not yet been identified.

» READ MORE: Jeff Sessions pushed out after a year of attacks from Trump

Attorney General Jeff Sessions submitted a resignation letter at President Trump's request Wednesday after more than a year of personal attacks from Trump.

Trump has inserted Matthew Whitaker, a Republican Party loyalist and until now Sessions' chief of staff, in his place. Whitaker now has authority to oversee the remainder of special counsel Robert Mueller's Russia investigation, an investigation he has previously spoken publicly about stymying.

Questions remain about Philadelphia native Deputy Attorney General Rod Rosenstein's future. Rosenstein had been overseeing the special counsel's work and leaders on both sides of the aisle are concerned about what these developments mean for the probe.

» READ MORE: Election 2018 takeaways: A realignment, a split, and messages for 2020

If lines at the polls were longer than you remember, you have a good memory: despite the rain, turnout was brisk all over the Philly region.

What have we learned from the results so far? The backlash to President Trump is real, but his messages still resonate in some key areas, writes reporter Jonathan Tamari. It looks like gun control really did motivate voters and contributed to victories in Pennsylvania, Virginia, and Nevada. And Republican Rep. Brian Fitzpatrick defied a local blue wave in Bucks thanks to centrist messaging and a week opponent.

In the meantime, Democrat Andy Kim has claimed victory over incumbent Republican Rep. Tom MacArthur New Jersey's Third District. MacArthur, however, has not conceded.

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Your Daily Dose of | Buck Buck 

Do you remember "buck buck, "deadbox," or "kick to wickie?" Trace the history of Philly's old street games and you'll find a story of the city itself.