Trump's decision has been closely held, and as with any presidential decision subject to last minute change.

But the machinery around the president is preparing for a Barrett “rollout” after he announces his pick, scheduled for Saturday at 5 p.m.

Barrett is widely known and well-liked by many in the White House and the Senate, and is viewed as both the easiest to confirm and biggest lightning rod for the right, given her controversial stance on abortion and deeply conservative religious beliefs.

Once it was clear earlier this week that McConnell had the votes regardless of the pick, "the cake was baked," one Senate aide involved in the process told Axios.

And because she's already been vetted, her nomination can move quickly.

Axios reported back in March 2019 that Trump had his eye on Barrett, telling confidants he was “saving her for Ginsburg” when her name came up during deliberations over replacing Justice Anthony Kennedy, who retired.

Behind the scenes: The way Barrett got on Trump’s Supreme Court list was simple. In late 2017, former White House counsel Don McGahn and conservative movement leader Leonard Leo walked into the Oval Office and presented Trump with five additional judges to supplement his 2016 list of potential Supreme Court picks.