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How Robert Mueller blew up Donald Trump's week

Washington(CNN) If Donald Trump thought he could end this week with a high note at the G20 summit, Robert Mueller's investigation certainly scuttled those plans. 

Hours before Trump boarded his plane to Argentina, a bombshell landed in Trumpworld with the news Michael Cohen had pleaded guilty to lying to Congress about -- and a sign Cohen is talking Trump's business deals with Mueller -- a previously stated "red line" for Trump.

Trump fired back -- from the air -- tweeting that the investigation is an "illegal Joseph McCarthy style Witch Hunt" and should be called off.

He also defended his actions on the campaign trail: "Even if he was right, it doesn't matter, because I was allowed to do whatever I wanted during the campaign."

Meanwhile, the field of would-be challengers to Trump is crystallizing, with more and more Democrats inching closer to announcing their intentions to run.

The Point: Best-laid plans of mice and men (and the Trump administration) often go awry, especially when Robert Mueller is involved. 

And here's a recap of this week in 21 headlines:

Monday:

Tuesday:

Wednesday:

Thursday:

Friday:

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