WASHINGTON (AP) -- Democrat Hillary Clinton is buying television advertising time in Republican-dominated Texas, hoping to tighten the presidential race in America's largest conservative state.

Clinton's campaign said Monday that a 30-second commercial will air for one week in Austin, Dallas, Houston and San Antonio, while also appearing online. Its cost wasn't released.

The ad touts the Dallas Morning News' endorsement of Clinton -- the first time the newspaper backed a Democrat for president since 1940.

Texas hasn't voted Democratic in a presidential race since Jimmy Carter in 1976. The Republicans, meanwhile, haven't lost a statewide office in Texas since 1994, the nation's longest political winning streak.

Some polls suggest the Texas race between Clinton and Donald Trump is getting closer. Texas' top Republicans leaders continue to vocally back Trump.