WASHINGTON — Congressional Democrats are reintroducing legislation to ban assault weapons but the measure faces long odds even after last month’s mass school shooting in Newtown, Conn.

The measure being unveiled Thursday is authored by Democratic Sen. Dianne Feinstein of California, who wrote the original assault weapons ban. That law expired in 2004 when Congress refused to renew it under pressure from the National Rifle Association.

An assault weapons ban is among the measures supported by President Barack Obama, who unveiled a package of gun safety proposals last week. But because of concerns among moderate Democrats it’s seen as a heavy lift in Congress, with measures such as beefed-up background checks more likely to pass.

There’s disagreement about the effectiveness of the original assault weapons ban.