WASHINGTON — No American president since Franklin Delano Roosevelt has won a second term in office when the unemployment rate on Election Day topped 7.2 percent.

Seventeen months before the next election, it is increasingly clear that President Obama must defy that trend to keep his job.

Roughly 9 percent of Americans who want to go to work cannot find an employer. Companies are firing fewer people, but hiring remains anemic. And the vast majority of economic forecasters, including the president’s own advisers, predict only modest progress by November 2012.

The latest job numbers, due Friday, are expected to provide new cause for concern. Other indicators suggest the pace of growth is flagging. Weak manufacturing data, a gloomy reading on jobs in advance of Friday’s report and a drop in auto sales led the markets to their worst close since August, and those declines carried over into Asia Thursday.