The defense team for President Donald Trump in his Senate impeachment trial has argued that freezing $391 million in military aid to Ukraine for two months weeks was not tied to the president’s requests that the Ukraine government announce investigations into Hunter Biden.

The Senate and the nation are to believe, instead, that the administration withheld the aid over concerns about corruption in Ukraine generally and allegations of inadequate burden sharing by other allies in Ukraine’s defense. This, despite the fact that the president had shown no prior interest in corruption, a review had found no corruption as a reason to stop the aid, and that European Union and European financial institutions had contributed more than $16.4 billion in grants and loans to Ukraine since 2014.

Evidence and testimony presented in the House impeachment hearings suggests the president’s real motivation was to get Ukraine President Zelensky to publicly announce an investigation into Hunter Biden’s service on the board of a Ukrainian natural gas company with a checkered record, Burisma, and by extension embarrass Trump’s potential rival in the 2020 election, former Vice President Joe Biden.

In other words, Trump was using funding approved by Congress to leverage foreign assistance in his re-election. It is why he was impeached.

Now the Senate and the nation have learned, during but apart from the impeachment trial, that a firsthand witness to the affairs in the White House can clarify that Trump, despite his denials, did want the aid held up until an investigation into the Bidens was announced. That witness is former National Security Advisor John Bolton. The information from Bolton that contradicts the core of the president’s defense is revealed in the unpublished manuscript of Bolton’s upcoming book, obtained by the New York Times.

Trump has denied saying that the aid was tied to a request for investigations. He dismissed any Bolton claim to the contrary as “only to sell a book.”

While we have in the past vehemently disagreed with the hawkish Bolton over issues of foreign policy, it is hard to imagine this longtime public servant lying about such profound matters to increase sales of a book.

But the best way to learn, assess and test what Bolton knows is to call him as a witness, under oath, in the impeachment trial. Given the pledges taken by the senators to impartially seek the truth, how can they not call a witness of such importance?

We urge Republican senators to place their duty above partisan politics and allow this critical testimony.

The White House has signaled it may try to block Bolton’s testimony, and that of any other current or former presidential aides, claiming executive privilege. This contention is absurd on its face. The Constitution gives the House of Representatives the power to issues articles of impeachment. The House has — for abuse of power and obstruction of Congress. The Constitution then calls for a Senate trial to determine whether a president should be convicted and removed from office.

These provisions were intended as a check on abuses by the executive branch. How could the Senate fulfill that role if not allowed to call witnesses with knowledge of the president’s actions? Certainly, the Founders did not intend to allow a president to interfere in a Senate trial on his own impeachment, anymore than a defendant in any trial would be allowed to determine who could testify.

There are no indications that Bolton’s testimony would enter into sensitive areas of national security. In the unlikelihood it did, Supreme Court Justice John Roberts, as presiding judge, could rule on admissibility and potentially move some questioning into closed session. But, again, this outcome seems unlikely.

A subpoena demanding Bolton’s testimony could be appealed, we suppose, to the federal courts. If so, the courts should act expeditiously in upholding the Senate’s authority to conduct the trial as it sees fit.

Would the Trump defense team respond by calling Hunter Biden? They may, even though their argument for his materiality is a strained one. As inappropriate as it may have been for Biden, whose father was vice president at the time, to take the Burisma position, it in no way justifies the shakedown scheme Trump was impeached for pursuing.

If Biden is called, Connecticut’s two Democratic senators, Chris Murphy and Richard Blumenthal, should have no complaints. Witnesses can either be called or they can’t.

One witness, however, is particularly critical to get the truth — John Bolton.

The Day editorial board meets with political, business and community leaders to formulate editorial viewpoints. It is composed of President and Publisher Timothy Dwyer, Executive Editor Izaskun E. Larraneta, Owen Poole, copy editor, and Lisa McGinley, retired deputy managing editor. The board operates independently from The Day newsroom.