In the battle unfolding in Congress between the Democrats and Attorney General William Barr, Im on the side of the United States Constitution. That means defending not only Mr. Barr but also President Trump. The two men stand on Americas legal bedrock.

Which is why Mr. Barr was able to make short work of his Democratic questioners at Wednesdays hearing in the Senate. His calm, straightforward testimony made it clear that he isnt the caricature the Democrats have been drawing of him.

And events arent the conspiracy the Democrats are still trying to validate, even after Special Counsel Robert Muellers finding that there was no collusion, actual or attempted, ­between Trumps camarilla and the Kremlin. Nor any prosecutable obstruction case.

Yet no sooner did Barr, under pressure for an early summary, send a sketch of Muellers report to Congress than the Democrats started suggesting he had spun the story in favor of the President. That was the guts of the hearing in the Senate.

The nastiest of the Democrats  Senator Patrick Leahy of Vermont  went so far as to suggest that Mr. Barr had misled Congress in his reporting of the investigation. He tweeted that Mr. Barr knew that Mueller had serious concerns about Mr. Barrs summary report.

So what? Mr. Mueller didnt accuse Mr. Barr of misrepresenting him. He complained that Mr. Barrs letter sketching the key elements of Mr. Muellers report didnt fully capture the reports context, nature and substance. What four-page sketch can fully capture a 448-page report?

It turns out that Mr. Mueller wanted the report released piecemeal. Mr. Barr overruled him. It looks similar to, say, a hapless middle-ranking editor (Mr. Mueller) caught between an activist staff (Mr. Muellers Clintonite investigators) and a hard-headed boss (Mr. Barr).

Happens all the time, even in the Justice Department. Prosecutors often disagree with investigators. Big whoop. Top brass frequently overrule them, too. Thats one of the things they are there for. Its why they get paid the big bucks.

Which brings it back to Trump. Hes the constitutional adult in this drama. Of all the people in this country  including our judges and members of Congress  Mr. Trump is the only one empowered and commanded to take care that the laws be faithfully executed.

Immediately after issuing that command, the Constitution ­ordains that the president shall commission all the officers of the United States. In other words, it is the president who must enforce the law, and only he gets to pick the staff to do so. While hes president, executive power flows from his very person.

No wonder Mr. Trump went into such rages at the suggestion that he cant  or shouldnt  fire the special counsel. For Democrats to suggest, as they continued to do in the Senate Wednesday, that it would be obstruction for Mr. Trump to fire Mr. Mueller is itself an obstruction.

Its just weird for Senator Kamala Harris to open the line of questioning she pursued Wednesday. She asked Mr. Barr whether Mr. Trump had suggested Mr. Barr prosecute anyone. Presidents dont usually do that, and Mr. Barr stumbled a bit on the question.

At the end of the day, though, what would be wrong had Trump made such a suggestion? Since the president alone is commanded to faithfully execute the laws, it isnt constitutionally kosher for Congress or a special counsel to try to restrict his freedom of action.

At one point Wednesday, Mr. Barr ­referred to Mr. Muellers letter to him as snitty. Senator Richard Blumenthal of Connecticut then asked Mr. Barr whether hed make available notes of one of his conversations with Mr. Mueller. Mr. Barr said he wouldnt.

So far, so good. Things would no doubt get nastier in the House, which was due to grill Barr Thursday, though he has reportedly declined the invite. The House has one enormous club that the Senate lacks, the power to initiate impeachment. Then, the power of the president to resist starts to fall away.

That was marked long ago by President Washington but also by President James Polk. He once said that when it comes to impeachment, the power of the House would penetrate into the most ­secret recesses of the executive branch.

It could, Mr. Polk added, command the attendance of any and every agent of the government, and compel them to produce all papers, public or private, official or unofficial, and to testify on oath to all facts within their knowledge. Thats the line Messrs. Barr and Trump are walking.

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This column first appeared in the New York Post.