Sen. Tim Kaine Timothy (Tim) Michael KaineBiden promises Democratic senators help in battleground states Second GOP senator to quarantine after exposure to coronavirus The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep MORE (D-Va.) is demanding that a secret document describing President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE’s understanding of his power to declare war be released, NBC News reported Friday.

Kaine requested that the memo be released in a letter sent to Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE on Thursday night. The 7-page memo has existed for months, but the administration has declined to make it public.

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“The fact that there is a lengthy memo with a more detailed legal justification that has not been shared with Congress, or the American public, is unacceptable,” Kaine wrote in the letter, which was obtained by NBC News.

“I am also concerned that this legal justification may now become precedent for additional executive unilateral military action, including this week’s U.S. airstrikes in Syria against pro-Assad forces or even an extremely risky ‘bloody nose’ strike against North Korea,” he continued.

Kaine has pushed for Trump to publicly state his legal reasoning behind the U.S. bombing in Syria last April in retaliation for President Bashar Assad’s use of chemical weapon against his own people.

Kaine, who sits on the Senate’s Armed Services and Foreign Relations committees, is among lawmakers who have said the move could undermine the congressional authority needed to declare war.

The request comes as the U.S. remains involved in Syria, and as Trump continues to threaten military action against North Korea.

Trump has repeatedly made threats against North Korea over its nuclear tests, promising last year that the country would be met with “fire and fury” if it threatened the U.S. The country has continued to carry out the tests.

Other Trump administration officials, including Secretary of Defense James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE and U.S. Ambassador to the United Nations Nikki Haley Nimrata (Nikki) Haley'The soul' versus 'law and order' Author Ryan Girdusky: RNC worked best when highlighting 'regular people' as opposed to 'standard Republicans' GOP lobbyists pleasantly surprised by Republican convention MORE, have suggested in recent days that the U.S. could remain involved in Syria and carry out more attacks over the purported use of chemical weapons in the country.