U.S. President Donald Trump reacts upon arriving to speak at a campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

Supporters react during U.S. President Donald Trump's campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

U.S. President Donald Trump arrives for a campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

U.S. President Donald Trump gives a thumbs up as he arrives for a campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

Supporters react while attending U.S. President Donald Trump's campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

U.S. President Donald Trump interacts with supporters at a campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

U.S. President Donald Trump walks up the stage to speak to supporters during a campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

U.S. President Donald Trump reacts while speaking during a campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

Supporters attend U.S. President Donald Trump's campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

U.S. President Donald Trump reacts during a campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

Supporters attend U.S. President Donald Trump's campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

U.S. President Donald Trump reacts while speaking during a campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

Supporters react during U.S. President Donald Trump's campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

U.S. President Donald Trump reacts while speaking during a campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis

A Keep America Great cap is seen atop a Christmas tree during U.S. President Donald Trump's campaign rally in Battle Creek, Michigan, U.S., December 18, 2019. REUTERS/Leah Millis