(CNN) - Sen. Elizabeth Warren tweeted on Friday evening that "Congress is complicit" in failing to start impeachment proceedings against President Donald Trump after the news broke that Trump had pressed Ukraine's President to investigate Democratic presidential candidate Joe Biden's son, according to a person familiar with the situation.
Asked by CNN at Saturday's Iowa Steak Fry as she was leaving the grill area what steps Congress needed to take, the Massachusetts senator said, "Impeachment, we need to start impeachment proceedings."
Warren, who is running for President, first called for impeachment proceedings in April after she read special counsel Robert Mueller's report on the investigation into Russian interference in the 2016 election.
Since then, she has repeatedly called for the House to begin impeachment proceedings but took it a step further Friday by calling Congress "complicit" in "failing to act."
"After the Mueller report, Congress had a duty to begin impeachment," she wrote in a tweet Friday evening. "By failing to act, Congress is complicit in Trump's latest attempt to solicit foreign interference to aid him in US elections. Do your constitutional duty and impeach the president."
She also wrote in a thread that the President "continues to commit crimes" because "he knows his Justice Department won't act and believes Congress won't either."
She told reporters after a climate change town hall Friday evening that Trump "continues to show that he has no regard for the law." She did not address Biden in her tweets or with reporters.
"The way to hold the President accountable is for Congress to begin an impeachment proceeding. Congress hasn't done that," she told reporters in Cedar Rapids. "And what the President has now demonstrated is that he thinks it's pretty clear he doesn't have to follow the law, and in fact can continue to commit high crimes and misdemeanors. He can go back to the well on exactly what he did before. And that is invite and profit from foreign interference in our election. It's time for Congress to step up and begin serious impeachment proceedings against this man."
Trump pressed Ukraine's President to investigate Biden's son during a call earlier this summer, a person familiar with the situation told CNN on Friday.
That call, which took place on July 25, a day after Mueller testified before Congress about Russian interference in US elections, was part of a whistleblower complaint submitted to the intelligence community inspector general, the source added.
The Wall Street Journal was first to report that Trump had pressured Ukrainian President Volodymyr Zelensky during the July phone call to investigate Biden's son, citing multiple people familiar with the matter.
CNN's Annie Grayer, Zachary Cohen and David Shortell contributed to this report.
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