And this is a monthly approval number so it’s not an anomaly.

PRINCETON, NJ — President Barack Obama’s job approval rating averaged 41% in September, tied with August for the lowest monthly approval average of his administration.

President Obama’s approval ratings predictably differ by party identification and ideology, ranging from a 79% approval rating among liberal Democrats to a 7% rating among conservative Republicans.

His current ratings among all these groups are lower now than earlier in his presidency, but he has lost proportionately more support among Republicans and less among Democrats.

As a result, the approval spread among these political groups has widened during Obama’s term. The accompanying chart displays these groups’ average yearly approval ratings of Obama, indexed to his national average for each year. Index values above 100 indicate that the group in question gave Obama a higher rating than the national average for that year; values below 100 show that the group gave him a lower rating than the national average for that year.

Obama’s indexed ratings among liberal, moderate, and conservative Democrats are proportionately higher now than in 2009, meaning these groups’ ratings of the president have stayed relatively high compared with other groups over time.

Moderate and conservative Republicans’ indexed ratings of Obama are lower now than in 2009, meaning his ratings among these groups have declined disproportionately compared with other groups. The spread in Obama’s ratings between Democrats and Republicans has thus expanded over time; therefore, political polarization has increased over the course of Obama’s term so far.