Democrats need to topple five Republicans to take over the Senate -- just four if they win the White House so their vice president can vote to break ties. Some of the most vulnerable Republicans are being challenged by women Democrats. After November, there could be more women Senators than ever before. And, the Senate really matters — as President Obama has learned all too clearly with issues including the confirmation of Supreme Court appointees. Bernie Sanders is back in action — with an agenda different from the Democratic National Committee's. We look at races around the country.