U.S. Sen. Bernie Sanders returned to Washington for meetings on Thursday with President Barack Obama and Senate Minority Leader Harry Reid as Democrats pressured him to end his presidential campaign and support Hillary Clinton after a hard-fought primary race.

Clinton, a former secretary of state, U.S. senator and first lady, secured enough delegates to secure the Democratic nomination this week and become the first woman to lead a major U.S. party as its presidential nominee.

Despite Clinton's commanding victories in California and New Jersey in presidential contests on Tuesday, Sanders vowed to carry his populist campaign to the Democratic National Convention in July, when the party's nominee is formally chosen.