Joe Biden caught plagiarizing — again. His campaign says they just forgot the citations on his climate plan.

Democratic presidential front-runner and former Vice President Joe Biden on Tuesday found himself once again in the middle of a plagiarism controversy. He and his campaign faced accusations of several instances of plagiarism just hours after releasing his "new" proposal to combat climate change.

What are the details?

Biden rolled out a purportedly fresh environment plan on Tuesday, while claiming that if he became a resident of the White House he would "go well beyond" what former President Barack Obama achieved during his tenure.

After the framework was released, however, eagle-eyed Americans found that the candidate's proposals weren't so fresh after all.

Liberal activist Josh Nelson was the first to throw a flag, Business Insider reported, pointing out on Twitter that Biden's "climate plan about carbon capture and sequestration includes language that is remarkably similar to items published previously by the Blue Green Alliance and the Carbon Capture Coalition."

Business Insider then picked up the baton and found another two lines in Biden's plan that were lifted from other authors' original work.

For example, Biden's proposal claims, "The average American sewage pipe is 33 years old, with many pipes dating back 50 or even 100 years." Business Insider pointed out that clean water advocacy group American Rivers states on its website that "the average American sewage pipe is 33 years old, with many pipes dating back 50 years or even 100 years," using the exact same language in the former vice president's script.

The Biden campaign explained to Business Insider that "several citations were inadvertently left out of the final version of the 22-page document," and, "as soon as we were made aware of it, we updated to include the proper citations."

Isn't there a history, though?

During Biden's 1988 presidential bid, it was discovered that he copied a speech from a British politician and falsely claimed that he was the first of his family to graduate from college. The former senator from Delaware also admitted to copying lines from a law journal while he was a student at Syracuse University, Business Insider noted.