DES MOINES, Iowa -- Hillary Clinton was always expected to get a late-campaign enthusiasm boost from the White House. The surprise is that it's not coming from the president.

On a star-studded team of campaign surrogates led by President Barack Obama, Michelle Obama has emerged as the most valuable player of Campaign 2016.

In a divisive political year, the first lady is wowing voters with her powerful rhetoric. She's also serving as the emotional centre for a candidate who isn't known for projecting warmth.

Last week, Mrs. Obama criticized Republican candidate Donald Trump for recorded boasts about making unwanted sexual advances toward women. She said Trump's comments had shaken her to her core.

She stepped in where Clinton couldn't, given the allegations of sexual wrongdoing against Clinton's husband that Trump has resurfaced.