Can any Republican truly challenge Trump?

First: Republican candidates got busy bruising each other last night in a chaotic debate marked by insults, prepared one-liners and plenty of pettiness. But it offered little clarity about who, if anyone, can beat Donald Trump? 

Plus: Today is day one of the impeachment inquiry into Joe Biden. Republicans promise a show and tell. Democrats ask, where's the evidence? 

And: President Biden is in Arizona to revive a 2020 and 2022 campaign theme that Democrats believe worked: MAGA extremists are a singular threat to American democracy. 

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