Portland, Ore. -- Speaking at a campaign rally Tuesday evening, President Obama called on Congress to pass a bill that would extend the Bush-era tax rates for families earning under $250,000 -- and let rates rise for everybody else.

"Tomorrow, the Senate is going to vote on a bill that says that if you earn less than $250,000 a year, your taxes will not go up next year by a single dime," Obama told supporters in Portland, Ore.

But the president didn't express high expectations for this Democrat-backed bill. Despite bipartisan support by senators of both parties in Congress, Washington is strongly divided this election year. Obama called the capital city "the only place where people agree on something and still can't get it done."

The Senate is poised to vote Wednesday afternoon to try to launch debate on the Middle Class Tax Cut Act of 2012 (S. 3412). Democrats say it will protect 98 percent of Americans from seeing their taxes go up next year, but charge that Republicans are holding things up, wanting legislation to extend the tax rates for everyone.

Obama says well off people like himself should pay a little extra. "I believe you can't reduce the deficit without asking folks like me who have been incredibly blessed by this country to give up a little bit of the tax cuts that they've been enjoying for a decade," Obama said.

Republicans including Mitt Romney say enacting only a partial extention, while letting rates rise for top earners, hurts many small business owners and would further impact economic recovery. "We don't think we ought to be playing Russian roulette with the American economy," Sen. Mitch McConnell, R-Ky., said Tuesday afternoon in Washington.

The Senate will hold a test vote on the bill Wednesday. The majority of the day will be dominated by debate on both sides of the isle. The Senate needs a 60-vote threshold to proceed with the bill.