Two former Trump allies jump into the race to challenge him

As the GOP primary field expands, its latest entries this week are marked by the candidacies of former Vice President Mike Pence and former Gov. Chris Christie (R-N.J.) — the head of the Trump White House transition team and formerly thought of as a top VP candidate. Amy Walter, publisher and editor-in-chief of the Cook Political Report, and Michael Kruse, senior staff writer for Politico, join Chuck to size up the developing primary.