Federal prosecutors implicated President Donald Trump in felonies for the first time in December, stating Trump directed illegal payments to two women who said they had affairs with him in an effort to protect his presidential campaign.

According to legal experts, perhaps the only reason Trump has not been charged with a crime is the fact he is president.

Trump has shifted from denying any knowledge of the payments Cohen made to characterizing them as a "private transaction," rejecting the notion he did anything illegal.

Trump has also rejected other accusations leveled against him, including obstruction of justice, and vehemently denies any collusion with Russia.

Since the special counsel Robert Mueller began investigating Russian election interference and the accusations that the Trump campaign colluded with the Kremlin, President Donald Trump has vehemently rejected the notion he did anything remotely illegal in relation to the 2016 election.

But federal prosecutors implicated Trump in felonies for the first time in December, stating the president directed illegal payments to two women who said they had affairs with him in an effort to protect his presidential campaign.

A sentencing memorandum released by prosecutors for the Southern District of New York in December said the president's former personal lawyer, Michael Cohen, made the illicit payments "in coordination with and at the direction" of Trump. Cohen was subsequently sentenced to three years in prison.

Read more: Here's a glimpse at Trump's decades-long history of business ties to Russia

Cohen had previously implicated Trump in the illegal payments, which represent campaign-finance violations because they were intended to influence the election, when he pleaded guilty to eight criminal charges in August. But the mid-December filing took things a big step forward, given federal prosecutors endorsed Cohen's allegations against Trump.

"With respect to both payments, Cohen acted with the intent to influence the 2016 presidential election," the filing stated. "Cohen coordinated his actions with one or more members of the campaign, including through meetings and phone calls, about the fact, nature, and timing of the payments ... And as Cohen himself has now admitted, with respect to both payments, he acted in coordination with and at the direction of Individual-1."

The memo added, "As a result of Cohen's actions, neither woman spoke to the press prior to the election."

"Individual-1" is Trump, and the memo puts him in an uncomfortable position as federal prosecutors have connected him to serious crimes. But there is a difference between being implicated in crimes and being formally accused of or charged with committing a crime.

The US Constitution does not say a sitting president cannot be indicted. Mark Wilson/Getty

According to legal experts, perhaps the only reason Trump has not been charged with a crime is the fact he is president. The US Constitution does not say a sitting president cannot be indicted, but it would go against Justice Department policy.

Bradley P. Moss, a Washington, DC-based lawyer specializing in national security, told INSIDER that "quite possibly the only reason the president has not been indicted (or at least been issued a target letter) by the federal prosecutors is because he is the president and the standing [Department of Justice] guidance is that a sitting president can't be indicted."

This puts the Justice Department in a "difficult position" given the "statute of limitations to indict [Trump] will have lapsed if he nonetheless wins reelection in 2020 and serves out a full two-term presidency," Moss explained.

The statute of limitations for campaign-finance law is five years from the date of the offense, so in this case that would be around fall 2021 (the payments were made in August and October 2016).

Accordingly, if the president is ultimately reelected, and the prosecutors believe "a credible prosecution would otherwise be brought" against him, Moss said, the likely result is that they'll submit a report to the attorney general "who will then have the option to forward that report to Congress for possible impeachment proceedings."

Moss added there is also the option of a sealed indictment, but said this would be an "illogical move" given many details surrounding the case are already public.

If the Justice Department believes it has a credible case against the president but can't move forward as a consequence of "institutional policy," Moss said, then it should refer the matter to Congress to "evaluate whether the circumstances warrant impeachment proceedings."

"That is how the system was designed to address the very real possibility of a president who has committed high crimes and misdemeanors and to ensure that a president is not 'above the law,'" Moss said. "It also makes it so that the serious matter of potentially removing a president from office has an aura of political legitimacy to it, in addition to legal legitimacy."

Similarly, Asha Rangappa, a former FBI special agent and Yale Law School lecturer, told INSIDER, "The short answer is that right now it is [Department of Justice] policy not to indict a sitting president."

Read more: Everything Michael Cohen told Mueller about the Trump campaign's contacts with Russia, according to the memo that could land Cohen a 'substantial' prison sentence

Rangappa added, "That is not settled law, however, and so it depends on whether they want to change or depart from that policy in the current circumstances — particularly since, unlike with previous special prosecutors/independent counsels, there is no direct way for [Robert Mueller] to report his findings to Congress or make them public."

Legally, Mueller is only required to submit his final report to Deputy Attorney General Rod Rosenstein, who is overseeing the investigation. Rosenstein is not obligated to make the report public or submit it to Congress.

There's also the possibility that Trump makes it to the 2020 election scot-free, but ultimately loses. If this occurs, he would lose the de facto presidential immunity and be far more susceptible to facing charges. His term of office would expire at noon on January 20, 2021, in the event Trump loses on Election Day in 2020.

As Jennifer Taub, a professor at Vermont Law School wrote in a recent op-ed for CNN, "Whether indicted as a direct violator of the Federal Election Campaign Act, aiding and abetting it, or conspiring to violate it, Trump could face a prison sentence ... Even if not indicted now, Trump has a big gamble ahead. He can hope he wins in 2020. But if he does not, a criminal trial most likely awaits him on the other side."

Read more: Federal prosecutors say 'Cohen deceived the voting public' and 'knowingly sought to undermine core institutions of our democracy,' explaining why he deserves prison time

Trump also has the option of resigning, allowing Vice President Mike Pence to take his place, and hoping for a presidential pardon for all federal crimes, Taub added. But even in this scenario there is no guarantee things would work out in Trump's favor.

Trump has shifted from denying any knowledge of the payments Cohen made to characterizing them as a "private transaction," rejecting the notion he did anything illegal. He also said his former personal lawyer is a liar who should be given a full sentence.

Read more: Democrats heighten calls for Trump's impeachment after bombshell report that says he instructed Cohen to lie to Congress

More recently, a bombshell BuzzFeed News report on Thursday alleged Trump instructed Cohen to lie to Congress about his involvement in a plan to build Trump Tower in Moscow.

Top Democrats in Congress have suggested that if the report is true it means Trump suborned perjury and obstructed justice, which are both serious crimes. But given the report remains unconfirmed it's difficult to say if Trump will ever face legal consequences in this regard.

Trump pushed back against the report by claiming Cohen is "lying to reduce his jail time."