Complex sentence: There have been 15 Democratic presidents: the first was Andrew Jackson, who served from 1829 to 1837, and the most recent is the current one, Barack Obama, the first African American president, who has served since 2009.
Split into simpler sentences: There have been 15 Democratic presidents: the first was Andrew Jackson, who served from 1829 to 1837. The most recent is the current one, Barack Obama, who has been in office since 2009.