(CNN) - Former Vice President Joe Biden's presidential campaign moved swiftly Tuesday to amend a climate change plan after questions arose about similarities between language in the proposal and progressive organizations' websites and letters.
"Several citations, some from sources cited in other parts of the plan, were inadvertently left out of the final version of the 22-page document. As soon as we were made aware of it, we updated to include the proper citations," Biden's campaign said in an emailed statement.
Biden released his climate plan -- which calls for $1.7 trillion in federal spending over 10 years to move the United States toward the goal of net zero greenhouse gas emissions by 2050 -- on Tuesday morning. Josh Nelson, the vice president of the progressive group CREDO Action, on Twitter pointed out two instances in which Biden's plan mirrored language from liberal organizations.
Later, the Daily Caller, a conservative news website, identified three other instances in which Biden's language was similar or identical to language used elsewhere -- on the news website Vox.com, on a federal government website and on the group American Rivers' website.
Biden's first bid for the presidency in 1988 was derailed when instances of plagiarism in campaign speeches and during law school came to light.
On Tuesday afternoon, Biden's campaign had added quotation marks and citations to the sections under scrutiny.
The document now includes new references to the Blue Green Alliance, the Carbon Capture Coalition, American Rivers, each of which are quoted directly, as well as one to "the U.S. Federal Government."
At least one of the sources included in the new citations -- American Rivers -- had already been cited in the original version of the plan that Biden's campaign had released.
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