TALLAHASSEE — When U.S. Rep. Alan Grayson entered the campaign for U.S. Senate, he was supposed to be an alternative for the Democratic Party's left wing.

But after a campaign that even progressives who supported Grayson say was badly managed, those hopes were dashed Tuesday night when Grayson gained only 18 percent of the vote against 59 percent for Rep. Patrick Murphy.

In a Wednesday interview, Grayson said "sewer money" used by Murphy and super PACs to tout an endorsement by President Barack Obama ultimately killed his Senate aspirations.

"Patrick has deprived Florida voters of a choice," Grayson said. "We have one avowed Republican (Rubio) running against a de facto Republican."

But one of Grayson's key supporters said the candidate had only himself to blame.

"I think it was Alan defeating Alan," said Susan Smith, president of the Democratic Progressive Caucus of Florida. "Not being a disciplined candidate, for example."

Never backed by the Democratic establishment, Grayson encountered additional challenges in fending off a controversy over off-shore hedge funds, which became the subject of a congressional ethics investigation, and allegations that he beat his second wife.

Grayson never set up a typical statewide campaign, and Smith says he didn't handle problems the way he should have.

Democratic strategist Steve Schale said Grayson hurt himself by not working to attract major donors. It costs money to run a successful campaign.

The result: Average voters didn't know who Grayson was.

"I do think that a progressive could absolutely win a statewide primary in Florida, but you're not going to win it by just firing off crazy emails and shoving reporters and hurling insults at people you don't like," Schale said, referring to a hostile encounter in July between Grayson and a Politico reporter.

In 31 counties, including Miami-Dade, Hillsborough, Pinellas and Broward, Grayson lost to Pam Keith, a Miami labor attorney in her first campaign for office.

But Grayson's political career is far from over, he insists. He plans to remain "a political leader," pushing senior issues and restoring rights to convicted felons who have served their sentences.

After all, Grayson lost his 2010 congressional re-election and then won the seat in 2012. Last night, he won in seven counties, including Orange and Osceola, the two that make up the congressional district he'll vacate in January.

And Smith believes Grayson could have something in his favor.

"Memories are short and people are reborn every day in the political world," she said. "Look at Marco Rubio for goodness sakes. He hated the Senate, he never wanted to be there and now he's going to be the nominee again."

Contact Michael Auslen at mauslen@tampabay.com. Follow @MichaelAuslen.