What Trump's 88% favorability among Republicans really means

Trump touts his high favorability poll numbers among Republicans.   The latest poll shows 88% among "Republicans."

But what does that actually mean in view of the number of people who have left the party because they dislike Trump?

If those who are disgusted by him enough to leave their party are no longer polled as "Republicans," then it would falsely appear that his approval is going up (as a % of those left) when, in fact, they may actually be going down if you include former Republicans who left the party because of Trump.

As a hypothetical explanation, let's say there were 1 million Republicans, 600,000 approved of Trump and 400,000 disapproved.   He would have a 60% approval rating (600,000 divided by 1,000,000). 

But then, if half the 400,000 who disapproved (200,000) left the party and all 600,000 who approved stayed in the party, then his approval rating among the remaining 800,000 "Republicans" would go up to 75% (i.e. 600,00 divided by 800,000).

The tricky part here is that you're not measuring a change in approval/disapproval of Trump;  you're measuring identity as a Republican.    For a truer measure of approval/disapproval, you need to poll everyone -- or at least the independents.

Ralph