WASHINGTON -- Less than a year after Inauguration Day, support for the Democratic Party continues to slump, amid a difficult economy and a wave of public discontent, according to a new Wall Street Journal/NBC News poll.

The findings underscored how dramatically the political landscape has changed during the Obama administration's first year. In January, despite the recession and financial crisis, voters expressed optimism about the future, the new president enjoyed soaring approval ratings, and congressional leaders promised...