President Obama's decision to endorse Hillary Clinton Thursday reignited concerns that the administration could shield the presumptive Democratic standard-bearer from any legal consequences that emerge from an FBI investigation into her private email use.

Republicans were quick to point out the conflicts of interest at play after Obama pledged his support to Clinton in a video message to her supporters.

"President Obama's official endorsement of an individual whose actions are the subject of an FBI criminal investigation is as disturbing as it is inappropriate," Rep. Darrell Issa, R-Calif., told the Washington Examiner.

"It reminds us once again this administration can't be trusted to be impartial, and the president's action taints the legitimacy of this very important inquiry," Issa added.

Critics have accused Obama of putting his finger on the scale of justice each time he has publicly weighed in on the probe. Obama did so for the first time in October 2015 when he dismissed the security concerns at the heart of the email investigation.

Reince Priebus, chairman of the Republican National Committee, said Clinton "put our national security at risk with her illicit email server" in a statement blasting the president's decision to throw his support behind the former secretary of state.

"Hillary Clinton is the first ever presidential candidate to be under an FBI investigation and her corrupt family foundation that has taken millions from foreign governments is an unprecedented conflict of interest," Priebus said.

Sen. John Cornyn said Thursday the president is caught in a "conflict of interest" when it comes to the FBI investigation and again urged the Justice Department to appoint an independent counsel to complete the probe.

The Texas Republican began pushing Attorney General Loretta Lynch to name a special prosecutor to the case in September of last year, arguing the Obama administration could not be trusted to investigate and potentially prosecute a former cabinet member and likely future nominee.

In November, dozens of House Republicans sent a letter to Lynch questioning the impartiality of the probe and demanding an independent counsel be assigned to the case.

Kendra Arnold, general counsel for the Foundation for Accountability and Civic Trust, said Obama's pledge of support for Clinton creates an inherent conflict of interest for the Justice Department.

"I think it's clear from his endorsement that he doesn't want the case to go to the indictment," Arnold said. "And it's obvious with his endorsement and his statements, that's definitely implying an outcome to [Lynch]."

Arnold noted the only way to mitigate the conflict of interest within the administration would be to appoint a special prosecutor to handle the case as it enters its final stages.

"Without that, there will always be that question about whether or not it was done fairly," she said.

Clinton has expressed confidence that the FBI will not uncover any evidence of wrongdoing in its months-long investigation of her handling of classified material.

However, the State Department inspector general announced last month that Clinton violated agency rules by setting up her own server. FBI officials have even suggested the investigation is focusing on classified email discussions of planned CIA drone strikes, which would mean highly sensitive intelligence passed through Clinton's unsecured network.