White House sources think Justice Anthony Kennedy, the Supreme Court's ideological fulcrum, may announce his retirement today, as the justices gather on the bench for the last time this term.

If that happens, Day 158 instantly becomes President Trump's biggest moment.

Trump's first Court appointment, of Justice Neil Gorsuch, was a one-for-one ideological swap for the late Justice Antonin Scalia. Replacing Kennedy would be even more historic and consequential: a momentous chance to edge the Court right, since Kennedy is the center of the Court — the one most willing to listen to both sides.

On a controversial case, both sides pitch to him. It's been called "Kennedy's Court." No one's predicting: Court watchers say no one knows, and Kennedy has said nothing publicly. He could well wait one more year: The Court buzz is that it'll be this year or next.

Be smart: Few domestic developments could more instantly and decisively change the national conversation — blotting out almost everything else, and vastly reducing the sting for conservatives is healthcare tanks.

A Washington wise man emails: "With two court appointments and maybe one more, Trump's presidency will be consequential even if he has few legislative achievements. This week may well demonstrate both."