The resignation of national security adviser Mike Flynn did not put to rest the many nagging questions surrounding the Trump administration's ties to Russia.

For example: Did President Trump or any of his associates have any improper - or possibly illegal - contact with Russia during the election campaign or transition? Did the Trump campaign collude with Russia against Hillary Clinton? Does Trump have any existing or pending business deals that could explain his deference to Russia and its president, Vladimir Putin? Do any of Trump's many companies owe money to any Russian banks or oligarchs? Does Russia have dirt on Trump that could be used to compromise his presidency?

Trump and his associates have denied any wrongdoing, but they have left unanswered another set of questions regarding the handling of the Flynn imbroglio. Do they know whether Flynn acted alone? Why did Trump wait days to dump Flynn after he was told about his communications with the Russian ambassador? Why was Vice President Pence left out of the loop and allowed to wrongly defend Flynn?

Those questions and many more threaten to hobble Trump's presidency after just one month in office. That is why there needs to be an immediate and independent investigation into this affair, including a release of Trump's tax returns to help clear the air.

Attorney General Jeff Sessions should appoint an independent special prosecutor to investigate. This is not a job for Sessions, who was an early and ardent Trump supporter and a senior adviser during the presidential campaign. Sessions also served with Flynn on the National Security Advisory committee during the transition from the Obama administration.

Sessions said he was "not aware of a basis to recuse" himself, but Justice Department rules prohibit an employee from participating in a criminal investigation or prosecution if there is "a personal or political relationship with any person or organization substantially involved in the conduct that is the subject of the investigation." The rules define "political relationship" as a "close identification with an elected official, candidate, political party, or campaign organization arising from service as a principal advisor or official."

Senate Democratic Leader Chuck Schumer also wants the Senate Intelligence Committee to lead a bipartisan inquiry with access to all "intelligence officials, transcripts, and documents" needed to answer critical questions and "make their findings public to the maximum extent possible."

With his party in the majority, Senate Republican Leader Mitch McConnell holds the key to any inquiry, but he has been cryptic about his plans, saying it is "highly likely" that the intelligence committee will investigate Flynn's talks with the Russian ambassador. Fortunately, some Republican senators support an investigation, including John Cornyn, Richard Burr, Lindsey Graham, Chuck Grassley, John McCain, and Pat Roberts.

The American public needs to know if its president has been in cahoots with Russia. If Trump has nothing to hide, he should be leading the charge to make sure all the facts are out.