Washington (CNN) I noted in this space last week that President Donald Trump had tied his highest approval ratings -- 45% -- in Gallup's weekly poll. A week can change a lot, apparently.

In Gallup's new weekly poll released Monday, Trump's approval rating had cooled off to 41% while his disapproval shot up 5 percentage points -- up to 55%. It's easy to ascribe Trump's approval fade to his disastrous past week in which he badly underestimated the damage done by his administration's "zero-tolerance" policy at the border. Trump eventually flip-flopped on his insistence that an executive order wouldn't solve the family separation crisis but, even then, legal and logistical questions remained.

But in truth, Trump's 41% approval could well be simply a return to normal. After all, Trump has averaged 39% approval in Gallup polling for the totality of his presidency to date. Trump's numbers among Republicans remain strong (90% approval last week, 87% this week) and his numbers among Democrats remain dismal (10% approval last week, 5% this week).

Seen through that lens, Trump's numbers last week are the exception; his numbers this week are the rule. And it's not totally clear how Republicans should feel about that fact.

On the one hand, Republicans remain extremely positive about Trump -- usually a sign the base of the party is activated and ready for the fall elections. On the other, the history of presidents under 50% approval in a midterm election is absolutely disastrous for the GOP. The average loss for the party in power is 36 House seats!

Trump's 45% showing last week had given some Republicans hopes that he might, maybe, make it close to 50% approval before November. Those hopes seem to have been short-lived. If you believe Gallup's long-term trend -- and you should -- the most likely place for Trump to wind up in November is somewhere between 39% and 42% in approval.