Merry Christmas! Obama kickstarts the festive season

The Library on the ground floor of the White House on Tuesday, Dec. 2, 2015, in Washington as Christmas decorations for 2015 are unveiled. (AP Photo)

Actress Reese Witherspoon served as host while Musicians Crosby, Stills and Nash, Kelsea Ballerini and Fall Out Boy also performed. (AP Photo)

President Obama closed the ceremony by taking over the microphone to help Santa Claus belt out Jingle Bells. (AP Photo)

First lady Michelle Obama with Miss Piggy, left, read 'Twas the Night Before Christmas for children on stage during the National Christmas Tree Lighting ceremony at the Ellipse in Washington. (AP Photo)

The ceremony of lighting up the National Christmas Tree was started as a community event back in 1923 which as now grown into a nationally televised event with celebrities performing. (AP Photo)

The President with his wife Michelle, daughters Malia and Sasha, and his mother in law Marian Robinson, together flipped a switch and illuminated the Christmas tree near the White House. (AP Photo)

In remembrance of the California victims, the U.S. flag flew at halfmast at the White House after President Obama's order. (AP Photo)

This is of course the most wonderful time of the year, but we would be remiss not to take a moment to remember our fellow Americans whose hearts are heavy tonight, who grieve for loved ones, especially in San Bernardino, California, Obama said. (AP Photo)

President Obama also appealed to his fellow Americans to come together as brothers and sisters a day after 14 people were killed in the deadly California shooting at San Bernardino. (AP Photo)

President Barack Obama lights the National Christmas Tree on Thursday kick starting the holiday season in the United States. (AP Photo)