How can you tell that 2010 is shaping up to be a really bad year for Democrats? Senator Pat Murray (D-WA) is at risk of losing her seat in the reliably-blue Evergreen State. In fact, the latest poll shows the three-term incumbent losing to not one but two potential Republican challengers.

Washington’s Senate race looks increasingly like a referendum on incumbent Democrat Patty Murray with two Republican candidates edging past her this month.

A new Rasmussen Reports telephone survey of Likely Voters in Washington State finds Republican hopefuls Dino Rossi and Clint Didier both earning 48% support in match-ups with Murray. She, in turn, picks up 45% of the vote against the two GOP challengers. Less than 10% of voters in both cases prefer some other candidate in the race or are undecided.

In June, Murray and Rossi were tied as they have been in virtually every survey this year. Since the beginning of the year, Murray has earned 46% to 48% of the vote, while Rossi’s support has ranged from 46% to 49%.

Incumbents that fall short of 50% at this stage of a campaign are considered potentially vulnerable, but worrisome for Murray is that this is her poorest showing of the year. She was reelected to a third term in 2004 with 55% of the vote.

Both Republican candidates easily carry Washington independents, with Rossi carrying them 60-29 and Didier pulling off a 57/32 margin. If the eventual Republican candidate holds the independent constituency, he or she will defeat Murray.

But how likely is it that either will hold independents? Very. The incumbent is viewed favorably by just 34% of independents and viewed unfavorably by 64% — an anemic figure that should have Murray sweating. Both Republican candidates are viewed favorably by a majority or plurality of independents, with Rossi being viewed favorably by 67%.

What’s driving this unforeseen result? The issues. Fifty-three percent of Washington voters favor the Arizona immigration law. Fifty-six percent oppose the Obama Administration’s lawsuit against the state.

Just 30% of voters believe the $787 billion stimulus package helped the economy. Fifty-eight percent of voters want tax cuts, while just twenty-eight percent want spending hikes.

This should have Democrats across the country extremely worried. If Pat Murray is trailing in deep-blue Washington, and deep-blue Washington is looking more and more conservative, how does that bode for candidates in Florida or Indiana?