Polls can change but a more reliable indicator that Reid is a goner is what his fellow Senators are doing:

The second- and third-ranking Senate Democratic leaders are doling out huge sums of cash, laying the groundwork for a leadership race should Senate Majority Leader Harry Reid lose reelection.

Sen. Charles Schumer (N.Y.), the vice chairman of the Democratic Conference, has been the biggest giver to Democratic Senate candidates, contributing $210,000 to colleagues and candidates.
During the same span, Majority Whip Dick Durbin (D-Ill.) has given $110,000 to Senate candidates.
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Both lawmakers gave the money through their leadership political action committees (PACs), which allies say is a sign that they are preparing for a possible leadership battle if Reid (D-Nev.) loses reelection, a prospect that is looking more likely.