Keir Starmer says that if he'd known Peter Mandelson had failed his vetting, he would never have appointed him US ambassador.
The PM told the MPs that civil servants in the Foreign Office had made a "deliberate decision" not to tell him, and that it "beggars belief" that he didn’t know.
This is a story full of political process, about whether rules were followed. But for many it may just boil down to why the Prime Minister did not ask more questions, especially when it concerned a man who had already resigned twice from government.
In this special extra episode Beth Rigby, Ruth Davidson and Harriet Harman give a full debrief on Keir Starmer’s Commons performance.
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And if you didn't know, you can also watch Beth, Ruth and Harriet on YouTube.