“Today, I vote to approve both articles, as my highest duty, and my greatest love, is to our nation’s Constitution,” Sinema said in a statement.

“The facts are clear; security aid was withheld from Ukraine in an attempt to benefit the president’s political campaign. While White House attorneys claim this behavior is not serious, it is dangerous to the fundamental principles of American democracy to use the power of the federal government for personal or political gain," Sinema added.

Sinema, who was elected to the Senate in 2018 from a state that Trump won two years earlier, was viewed as one of three Democratic senators who could potentially vote to acquit Trump on the two House-passed articles of impeachment: abuse of power and obstructing Congress' investigations into the president's decision to delay Ukraine aid.

But she warned that the decision to acquit Trump paved the way for future presidents using the Senate's votes "as a guide to avoid transparency and accountability to the American people. That should be gravely concerning to all of us."

The decision by the three senators deprived the White House and Republicans of what they had publicly predicted for months would be a bipartisan acquittal, similar to the two impeachment votes in the House.

Her moderate leaning has frustrated progressives, both in Arizona and nationally. Arizona progressives floated trying to censure Sinema late last week before backing down.

Sinema's moderate streak was put in the spotlight Tuesday night when she was seen standing and applauding Trump during moments of his State of the Union address, including a stretch on opportunity zones when most of her Senate Democratic colleagues remained seated and stoic.

Unlike Manchin and Jones, Sinema does not do routine hallway interviews with reporters around the Capitol, proving little insight into her thinking during the months-long impeachment fight.

Sinema telegraphed that she would not be discussing the trial while it was ongoing when she released a statement through a tweet before senators were sworn in saying that she "will not comment on the proceedings or facts until the trial concludes."

"I will treat this process with the gravity and impartiality that our oath demand," Sinema said at the time.

Updated at 4:23 p.m.