WASHINGTON — President Barack Obama is targeting vital North Carolina and Virginia this week, as he kicks off a three-day bus tour that is as much about campaigning for his jobs bill as it is shoring up support in two southern states he wrested from Republican control four years ago.

Pres. Obama’s 2008 victories in North Carolina and Virginia were due in large part to the states’ changing demographics and his campaign’s ability to boost voter turnout among young people and African-Americans. But nearly three years after his historic election, the president’s approval ratings in both states are sagging, in line with the national trend.

A Quinnipiac University poll out earlier this month put Pres. Obama’s approval rating in Virginia at 45 percent, with 52 percent disapproving.

The president’s bus tour comes as the battle in Washington over his jobs plan enters a new phase. While Pres. Obama had demanded lawmakers pass the $447 billion jobs measure in its entirety, Senate Republicans have blocked those efforts, leaving the president and his Democratic allies to fight for the bill’s proposals piece by piece.

Since announcing his plan for putting Americans back to work last month, Pres. Obama has been traveling the country trying to build public support for his initiatives.