(CNN) Poll of the week: A new national Gallup poll finds that 39% of Americans approve of the job Donald Trump is doing as president, while 57% disapprove.
That poll is in line with the average poll that shows Trump's approval rating is in the low 40s among all adults as well as voters specifically.
What's the point: We've still got five months until the general election, which, in theory, is plenty of time for the race for president to change. Indeed, horserace polling has sometimes shifted considerably between this point and Election Day.
Presidential approval ratings, however, haven't historically moved much from June of an election year to Election Day.
It seems quite likely at this point that Trump's approval rating is going to be south of 50% and his net approval rating (approval - disapproval) to be negative when people vote. That should be deeply troubling to Trump, given the strong link between approval ratings and reelection chances.
There have been 13 presidents who have run for another term in the polling era (since 1940). For each of those presidents, I compared their average Gallup (or, in the case of 1944, the Office of Public Opinion Research) June approval rating and their estimated approval rating on Election Day.
The average president has seen his approval rating shift by just 3 points from now until the election. That would only get Trump into the mid 40s at best. Trump's approval rating was similar during the 2018 midterms, when his party lost control of the House.
Net approval ratings tell the same story. The average president had his net approval rating shift by only 6 points from this point forward. Given Trump's net approval rating is in the negative low to mid-teens, a 6-point improvement would land him with a net approval around -7 to -10 points on Election Day. Again, that's about where he was during the 2018 midterms.
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Trump, though, isn't finished quite yet. It is possible for a president's ratings to shift around. Harry Truman saw about a 20-point increase in his net approval rating in the final five months of the 1948 campaign. On the other end, Lyndon Johnson's net approval rating declined by around 15 points in the final months of the 1964 election.
Still, we're only talking about two presidents out of 13 whose net approval rating moved by more than 10 points in the final five months of the campaign. One of those two went in the wrong direction for the president. Trump needs his net approval rating to climb by more than 10 points to reach a positive net approval rating.
Trump's fate against former Vice President Joe Biden won't be perfectly correlated with his approval rating, but it will be highly correlated. In our last CNN/SSRS poll, more than 90% of Trump approvers said they'd vote for Trump. More than 90% of disapprovers said they'd vote for Biden.
One previous estimate from FiveThirtyEight's Nate Silver suggested that a president with a 40% approval rating in the June before the election had only about a 20% chance of winning the upcoming election. That's largely jibes with more sophisticated models that take into account a slew of indicators.
Can Trump be one of the 20%? Obviously. Don't round 20% down to 0%.
Remember, though, that Trump's approval rating has been steadier than any president before him. There's no particularly strong reason to think he'll get a larger than average boost in his approval rating and therefore his reelection chances.
The inability for Trump to move his own numbers is probably why he goes after Biden so much. Biden's less defined than Trump, and dragging Biden down may be the only chance Trump has to win.