US Democrats Head to Convention to Acclaim Clinton Presidential NominationU.S. Democrats gathered Sunday for their national convention, set to acclaim former U.S. Secretary of State Hillary Clinton as the party's 2016 presidential nominee, the first time a major U.S. political party is picking a woman as its standard bearer. The convention opens Monday in Philadelphia, Pennsylvania, known as the City of Brotherly Love, but it is starting on a discordant note. WikiLeaks disclosed nearly 20,000 emails from Democratic Party leaders over the last year and a half that showed how they mocked and criticized the upstart campaign of Vermont Senator Bernie Sanders, while he was waging an unexpectedly tough challenge to Clinton over months of state-by-state contests for the nomination. One of the emails suggested Sanders might be an atheist, even though he embraces his Jewish heritage. Sanders, in a CNN interview Sunday, called the comments in the emails "outrageous," but said it was "not a shock to me." He added, "It's what we talked about six months ago, that the [Democratic National Committee] was supporting Hillary Clinton and was opposed to my campaign." Some Democratic leaders called for the resignations of party officials — including Democratic chairwoman Debbie Wasserman Schultz — who made objectionable comments about Sanders in what they thought were private emails. Sanders has since endorsed Clinton and is speaking Monday at the convention on her behalf, as is first lady Michelle Obama. Sanders said he will "do everything I can to make sure" Donald Trump, the Republican nominee, does not win the November national election to pick the successor to President Barack Obama when he leaves office next January. A fixture on the American political scene for decades, Clinton is headed to the party's quadrennial convention after naming Virginia Senator Tim Kaine as her vice presidential running mate. Clinton, the wife of former President Bill Clinton, told cheering supporters Saturday in Miami that Kaine is ready to become president if she were to die in office. He is "everything that Donald Trump and [his Republican running mate] Mike Pence are not," she said. The Democratic contender said her party's convention "will offer a very different vision for our country" than Trump did at last week's Republican national convention. Clinton said her campaign is "one that is about building bridges, not walls, embracing the diversity that makes our country great." Trump: US must be sharp, vigilant, strong Republicans, over months of contests throughout the country, picked Trump over 16 other challengers, many of them seasoned politicians. That made the billionaire real estate tycoon and one-time television reality show host the first major U.S. party presidential nominee in more than six decades to claim a major party's nomination without previously having been elected to any public office. Trump has called for building a wall on the U.S.-Mexican border to thwart the stream of undocumented migrants from entering the country. He told NBC's Meet the Press show Sunday that people coming from countries where terrorist attacks have occurred, including staunch U.S. ally France, may need to be subjected to "extreme vetting" before being allowed to enter the United States. "Maybe we get to that point," Trump said, adding, "We have to be smart and we have to be vigilant and we have to be strong." In the interview, Trump acknowledged that critics viewed his presidential nomination acceptance speech as "a little dark," but said he "thought it was very optimistic" because "we're going to fix the problems." He defended his comments last week questioning whether a would-be President Trump would defend the other 27 NATO allies if they were attacked — a bedrock principle of the U.S.-European military alliance since the end of World War II — if they were not spending enough money on their own defense. Speaking to CBS News Sunday, President Obama said Trump's comment concerning NATO is another sign of his "lack of preparedness" on foreign policy issues. Trump has said Clinton's record as the top U.S. diplomat from 2009 to 2013 "has been a disaster." Trump and Clinton both are viewed unfavorably by more than half the American electorate, polls show, with Trump more so than her. She holds a slight edge in national political surveys over Trump three and a half months before the election.