Measured according to 538:

https://projects.fivethirtyeight.com/polls/favorability/donald-trump/r/

The exact metric measured is "favorable" (and not "net favorable"). On February 8, 2024, Trump's "favorable" according to 538 is 78.5%. (His "unfavorable" is 19.5%, and his "net favorable" is +59.0%.)

The resolution decision will be made at any time the favorability goes below 60%, or as close as possible to the time of death (even if that excludes surveys from before the death that have not yet been added to 538).

If 538 no longer aggregates data on Trump's favorability among Republicans at the time of Trump's death, then a suitable replacement will be found (with consultation from the community). The core of the idea is to measure the general approval and loyalty of Republicans toward Trump over time.