A former top aide to President Donald Trump is appealing for contributions to a new legal defense fund, as ex-National Security Adviser Michael Flynn confronts possibly serious legal troubles involved in the ongoing investigation into Russian interference in the 2016 elections, and ties to Mr. Trump's campaign.

"We deeply appreciate the support of family and friends across this nation," Flynn tweeted on Monday morning, announcing that his brother and sister had created a legal defense fund "to help pay my legal defense costs."

Flynn, who was forced out of his post as head of the Defense Intelligence Agency under President Obama, was a familiar presence on the campaign trail for President Trump, later moving into a key role in Mr. Trump's inner circle after his victory in November 2016.

But once Flynn was officially on board in Trump Administration, he did not last a month at the White House, after questions were raised about his contacts with the Russian Ambassador to the U.S. during the Trump transition, along with separate lobbying activities.

Flynn's legal troubles have only seemed to grow in recent months - not only involving questions of what he discussed with the Russian Ambassador, but also lobbying efforts involving the government of Turkey, and questions about contacts with other foreign governments.

Also, there have been reports that Flynn's son, Michael Flynn, Jr., is under scrutiny as well by Special Counsel Robert Mueller.

"I believe the truth will prevail," the younger Flynn wrote about his father on Twitter this morning. "Hope others out there feel same."

Flynn's son has repeatedly denied he could be a subject of the same probe that has focused on his father.

Flynn's son has also used his Twitter account to attack Gen. H.R. McMaster, who replaced Flynn as President Trump's National Security Adviser, sending out tweets that say McMaster is unqualified to hold that post.

Flynn, Jr. also continues to press the discredited "Pizzagate" conspiracy, which claimed that top aides to Hillary Clinton ran a child sex ring out of the basement of a neighborhood Washington, D.C. pizza parlor.

The elder Flynn has said little about the investigation. His tweets today were his first since December of 2016.