Hillary Clinton welcomes Sanders into the race

Washington (CNN)Hillary Clinton played down tensions with her first rival for the Democratic presidential nomination, Vermont Sen. Bernie Sanders, in a tweet welcoming him into the race Thursday.

"I agree with Bernie. Focus must be on helping America's middle class. GOP would hold them back. I welcome him to the race," she tweeted, signing the post "-H" to signal it was sent by Clinton herself and not an aide.
It was the first acknowledgment from the former secretary of State of the challenge since Sanders announced Wednesday night that he would be entering the contest. And it was a marked effort to downplay the divide within the Democratic Party that contributed to Sanders' decision to launch a bid, between progressives clamoring for a challenger to Clinton and the large majority of Democrats who support her for the nomination.
    Clinton has maintained a decisive, double-digit lead in every survey of the prospective Democratic presidential field, drawing from 50-70% support among Democrats. But progressives remain wary of her candidacy, as they see her as too close to Wall Street.
    While Sanders isn't their first choice — progressives have expressed a strong preference for Massachusetts Sen. Elizabeth Warren, who remains adamant that she won't run — he offers the movement a useful foil for Clinton who could force her to the left on a number of key issues, including his pet crusade, big money in politics.
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    But his entry into the race poses risks for the Democratic Party as well, if the party infighting overshadows the contrast with Republicans that Democrats are hoping to draw in the race. Sanders, for his part, has indicated he has no intentions to pull punches in the race. During an interview with ABC News, Sanders called foreign donations to the Clinton Foundation a "very serious problem."
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    "It tells me what is a very serious problem," he said. "It's not just about Hillary Clinton or Bill Clinton. It is about a political system today that is dominated by big money. It's about the Koch brothers being prepared to spend $900 million dollars in the coming election."
    Sanders has promised to eschew any donations from billionaires, and during a later interview with CNN's Wolf Blitzer, said it was "vulgar...that we're having a war of billionaires."
    He also highlighted his opposition to the Iraq War, which Clinton voted to support. He said he'll make his opposition to the Keystone XL pipeline and his intense focus on climate change key issues in his campaign.