The investigation of President Trump took an ominous turn last week as federal prosecutors effectively accused Trump of directing his former fixer, Michael Cohen, to violate campaign finance laws in an attempt to influence the outcome of the 2016 election, while secretly seeking to do business in Russia well into his presidential campaign.

Trump continues to dismiss the gathering legal cloud with a barrage of fact-free tweets. But the mounting revelations underscore the need for the public to see Trump’s tax returns, and warrant the need for Congressional hearings once Democrats take control of the House next month.

House Republicans abdicated their Constitutional responsibility to act as a check and balance to the president the past two years. They all but admitted their willful failure before last month’s election by reportedly compiling a spreadsheet of the more than 100 possible investigations Democrats could launch when after taking control of the House.

The list included: Trump’s tax returns; his dealings with Russia; his family business, including whether it is complying with the Constitutions emoluments clause; and payments to Stormy Daniels.

The documents filed by federal prosecutors last week as part of the sentencing recommendations for Cohen, and Trump’s former campaign manager, Paul Manafort, are damning.

“Cohen sought to influence the election from the shadows,” prosecutors wrote. “He did so by orchestrating secret and illegal payments to silence two women who otherwise would have made public their alleged extramarital affairs with Individual-1.”

Prosecutors added that Cohen “acted in coordination with and at the direction of Individual-1.”

Individual-1, of course, is Trump.

The filings also undermine Trump’s claim that he has had “no dealings with Russia.” Cohen admitted the Trump Organization secretly pursued a project to build a Trump Tower in Moscow at least as late as June 2016 - the same month Trump campaign officials met with a Kremlin-connected lawyer who promised to provide them dirt on Hillary Clinton.

BuzzFeed reported that, as part of the 2016 negotiations, Trump planned to give Russian President Vladimir Putin a $50 million penthouse in his Moscow tower. At least 16 Trump associates have had contacts with Russians during the campaign or transition, according to CNN.

In last week’s court filing, special counsel Robert Mueller said Manafort lied to prosecutors on at least five different matters, including his interactions with Konstantin Kilimnik, a business associate with ties to Russian intelligence, who Manafort called his “Russian Brain.”

Famed Watergate reporter Carl Bernstein said Mueller’s latest court filings show Trump is “boxed in,” and impeachment proceedings seem likely. The top legal analyst for Trump-friendly Fox News, went so far as to say Trump could be indicted while in office.

A bipartisan group of 44 former senators said the United States is “entering a dangerous period,” and urged current and future Senate members to put aside their political ideologies and defend America’s democracy.

As the Mueller investigation proceeds, Congress must also do its duty, starting with examining Trump’s tax returns. As former President Richard Nixon said during Watergate: “People have got to know whether or not their president is a crook.”