WASHINGTON (Reuters) - The U.S. Justice Department moved closer to a politically sensitive prosecution of former top FBI official Andrew McCabe on Thursday by rejecting a request from his legal team to drop the case, according to two sources familiar with the investigation.

The notice indicates that the department could soon bring criminal charges against the FBI’s former No. 2 official, who has endured years of criticism by President Donald Trump after playing a key role in the investigation into the Trump campaign’s ties to Russia in the 2016 election.

McCabe has said those attacks are part of an effort to undermine law enforcement and intelligence professionals. He has sued the Justice Department, arguing that he was fired for political reasons.

McCabe’s lawyers urged Justice Department officials not to bring charges stemming from an internal investigation that found he misled investigators about his contacts with news media.

They were told on Thursday that the Justice Department had rejected their appeal, according to two sources familiar with the decision who spoke on condition of anonymity.

The Justice Department and the U.S. Attorney’s Office for the District of Columbia, which would prosecute the case, both declined to comment.

A lifelong Republican who worked at the FBI for 20 years, McCabe played a crucial role in the bureau’s investigations of Democratic presidential candidate Hillary Clinton and Russian interference in the 2016 U.S. election.

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In campaign speeches, interviews and tweets, Trump has accused McCabe of conflicts of interest because his wife Jill McCabe, a Democrat, received donations for an unsuccessful 2015 Virginia state senate campaign from a Clinton ally.

McCabe was fired in March 2018, just hours before he was due to retire, after the Department’s internal watchdog issued a report saying he misled investigators with the Inspector General’s office who were trying to determine whether he improperly shared information with a news reporter during the 2016 presidential election.

McCabe has said he tried to answer questions about the incident truthfully, and tried to clarify his responses when he though he had been misunderstood.

McCabe sued the Justice Department last month, arguing that he was improperly fired for his refusal to “pledge allegiance” to Trump.

McCabe briefly served as the acting head of the FBI after Trump fired his boss, James Comey, in May 2017. He told CBS News that he strengthened an investigation into the Trump campaign’s ties to Russia during that time out of fears that Trump or other administration officials would try to quash it. The Justice Department appointed Special Counsel Robert Muller to head the investigation shortly thereafter.

Trump has repeatedly urged the Justice Department to investigate McCabe, Comey, Mueller and other law-enforcement officials involved in the investigation, accusing them of political bias and conflicts of interest.

While Attorney General William Barr has authorized several investigations into the origins of the Russia probe, McCabe would be the first senior official to face criminal charges.

The Justice Department declined to prosecute Comey after the Inspector General’s office found that he had improperly handled memos he wrote about his one-on-one meetings with Trump before he was fired.

The Justice Department has also declined to prosecute other employees who were found to have made false statements to the Inspector General’s office - including a senior administrator who lied about looking at pornography on his government computer.