PORTSMOUTH, NH - Democrat Bernie Sanders endorsed former rival Hillary Clinton for president in a belated show of party unity on Tuesday, saying it was critical that Democrats come together to defeat Republican Donald Trump in the Nov. 8 election."She will be the Democratic nominee for president, and I intend to do everything I can to make certain she will be the next president of the United States," Sanders told a raucous crowd that included plenty of vocal Sanders supporters.Five weeks after Clinton clinched the Democratic presidential nomination, the US senator from Vermont ended his upstart campaign and joined her at a rally in Portsmouth, New Hampshire, to put their bitter primary battle behind them."I have come here to make it as clear as possible as to why I am endorsing Hillary Clinton and why she must become our next president," Sanders said.Sanders' endorsement brought the most prominent holdout in the party's liberal wing into Clinton's camp less than two weeks before the opening of the Democratic National Convention in Philadelphia, where Clinton is expected to become the party's nominee.Clinton hopes the joint appearance will help her win over Sanders supporters, some of whom carried Sanders signs into the rally and frequently drowned out her supporters. In recent Reuters/Ipsos polling, only about 40 percent of Sanders backers said they would back Clinton, and the crowd at Tuesday's rally made it clear she still had work to do."I am absolutely certain I will not vote for Hillary Clinton," said Gale Bailey, a Sanders supporter and an unemployed graphic designer from Rochester, New Hampshire, who attended the rally in a Sanders T-shirt."She's a crook, and I'm not going to vote for a crook," Bailey said, adding that she would write in Sanders' name on the November ballot.