Sanders discusses next steps with Obama after Democratic primaries

WASHINGTON (Reuters) - U.S. Senator Bernie Sanders returned to Washington for high-level talks on Thursday, including a meeting with President Barack Obama, as Democrats pressured him to end his presidential campaign and support Hillary Clinton after a hard-fought primary race.

Clinton, the former secretary of state, won 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 her 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.

Obama, who is expected to endorse Clinton soon, welcomed Sanders to the White House, chatting and chuckling as they walked into the Oval Office. Sanders will meet with Senate Minority Leader Harry Reid, a Democrat, in the afternoon.

The Sanders campaign, which waged an unexpectedly strong challenge to a better-known and better-funded Democrat, has decried what it called Clinton's anointment by the party establishment and the media.

Obama said in an NBC interview pre-taped on Wednesday that he hoped divisions between Democrats would start to heal in coming weeks now that Clinton has clinched the party's nomination for the Nov. 8 presidential election.

"It was a healthy thing for the Democratic Party to have a contested primary," Obama said at a fund-raiser in New York City later on Wednesday

Senior Democrats are seeking a delicate balance between the need to unite behind Clinton in the looming battle against Republican candidate Donald Trump and not alienating Sanders and his supporters.

U.S. Senator Elizabeth Warren, like Sanders a progressive and fiery critic of Wall Street, is preparing to endorse Clinton in the coming weeks after staying neutral in the Democratic primary, people familiar with her thinking told Reuters.

Republicans, meanwhile, are grappling with controversy over

Trump's attacks on Mexican-American U.S. District Judge Gonzalo Curiel, who is overseeing fraud lawsuits against the billionaire's defunct real estate training school.

Former House of Representatives Speaker Newt Gingrich told reporters on Thursday that Trump's comments were "fine." But he suggested Trump change tactics toward making more measured remarks as he did in a speech after primary elections this week.

"I think he has to continue what he did Tuesday night with the specific speeches aimed at big topics drawing a clear distinction between where he is and where Hillary is," Gingrich said.

"I think if he does that, the odds are very high he's going to win."

Both Clinton and Trump have begun to take clear steps toward the general election, planning events in key swing states. Each will hold rallies in Pennsylvania and Ohio early next week, with Trump also campaigning in Florida this weekend.

(Reporting by Emily Stephenson; Writing by Doina Chiacu and Megan Cassella; Editing by Bill Trott and Alistair Bell)