The back-to-back bad poll numbers come as Rivera fends off a federal investigation into whether he helped steer tens of thousands of dollars to an opponent challenging Garcia in the Aug. 14 Democratic primary.

The opponent, political newcomer Justin Lamar Sternad, is cooperating with the FBI, which is examining whether his federal campaign finance forms were intentionally misleading when they initially failed to report $47,000 in secret money linked to Rivera.

Rivera has denied wrongdoing.

The congressman is also under a separate federal investigation that stemmed from a secret $500,000 payment from a dog track. Records show he helped steer the payment to a company controlled by his mother. Rivera narrowly avoided 52 state charges linked to the payment. Prosecutors said the laws he might have broken were vague or the statute of limitations had expired.

Javier Correoso, campaign manager for Rivera, told The Herald that he would never be involved in a secret campaign.

“I don’t know who Lamar Sternad is. I absolutely had no involvement in the Sternad campaign ... Everything I learned came from the newspaper. This was a surprise to me.”

Correoso, who also ran Rivera’s 2010 campaign, said he hasn’t spoken to Rivera about the Sternad campaign.

“My focus right now is defeating Joe Garcia,” Correoso said.

Meanwhile, the Democratic Congressional Campaign Committee has reserved about $1.5 million worth of TV ad time, much of which could be used for Garcia. In contrast, the National Republican Congressional Committee has earmarked no money for Rivera.

But Republican insiders say that Rivera — a tough campaigner who excels in constituent services — won’t be easy for Garcia to beat, regardless of what the polls say. And the NRCC hasn’t written him off entirely, either.

“We don’t base our decisions on one poll alone and we’re closely watching this race,” said NRCC spokesman Nat Sillin.

Miami Herald staff writer Patricia Mazzei contributed to this report, which has been updated.