Former President Barack Obama is kicking off a campaign blitz Thursday in Pennsylvania, aiming to rally support for Vice President Harris in battleground states as she makes her final plea to voters with just under a month left before Election Day.

Obama's stop in Pittsburgh marks his debut as a battleground-state surrogate in the 2024 presidential election. He's expected to visit other swing states before Election Day, too.

He and former first lady Michelle Obama endorsed Harris in July, vowing to do everything they could to help her win the White House. Both have remained popular since the former president left office in 2017, and both addressed the Democratic convention in August.

"Kamala Harris won't be focused on her problems, she'll be focused on yours," Obama said in a speech at the convention. "As president, she won't just cater to her own supporters and punish those who refuse to kiss the ring or bend the knee. She'll work on behalf of every American. That's who Kamala is."

Obama has remained a key figure in the Democratic party since he left office in 2017, and had remained silent amid the calls for his vice president, President Biden, to drop out of the race, although there were reports that Obama had privately expressed concerns about Mr. Biden as the nominee. Mr. Biden ultimately dropped out of the race in July, backing Harris.

Obama and Harris have a long relationship, dating back to his run for Senate 20 years ago. Harris then backed Obama's history-making run for the White House, knocking on doors in Iowa.

While Obama rallies support for Harris in Pennsylvania, the vice president will be in Nevada, another key battleground, participating in a town hall event hosted by Televisa Univision before returning to Pennsylvania on Monday.

Harris is expected to hold a campaign rally in Erie, marking her first visit to the bellwether county since launching her presidential run.

But she has traveled to Pennsylvania over a dozen times in 2024, including seven since announcing her bid. Her surrogates, second gentleman Doug Emhoff, vice presidential nominee and Minnesota Gov. Tim Walz and Minnesota first lady Gwen Walz, have also been campaigning in the state.