The US president has campaigned at more than 20 rallies this month, underlining Republican concerns about losing control of Congress for the final two years of his presidency.
Obama, the last Democratic president to serve two terms, had kept a relatively low public profile until the past week, during which he has delivered blistering speeches criticising Trump.
"There is a moral component to the choices we face right now," Obama said in Georgia on Wednesday.
"We are not going to fix the system that's broken, we're not going to unrig our economy, so long as we've got a culture where anything goes, where people in the highest offices of the land think it's OK to lie and cheat and bully ... where money is deemed the only measure of our worth."
Trump told a crowd in Ohio that the "White House is beautiful" as he continues renovations, taking a jab at Obama's criticisms of them.
Obama ripped into Trump's focus on renovations over the weekend, telling a crowd in Ohio: "He's got the White House looking like Saddam Hussein opened a Cheesecake Factory."
Trump defended his decor and said Obama left the property deteriorated.
"The White House, I think, is the number one symbol of our country and we can't have a White House with broken windows, with broken stone that hasn't been painted in 30 years," Trump said.
Trump also attacked Democratic former Senator Sherrod Brown, who is challenging Republican Senator Jon Husted, for supporting immigration policies the president said had overwhelmed Springfield, Ohio, with Haitian migrants.
"The town went to hell," Trump said.
The billionaire spread false claims during the 2024 presidential campaign that Haitian immigrants in Springfield were eating cats and dogs, allegations local officials repeatedly said were untrue.
Enthusiastic crowds have cheered Trump at rallies throughout the campaign, but hundreds of protesters lined his motorcade route in rural Chillicothe, Ohio, raising banners that read, "Republican against Trump," "Grab them by the ballot" and "GOP: Guardians of pedophiles."
During Wednesday's rally, protesters interrupted Trump several times, including at least one who shouted about deceased convicted sex offender Jeffrey Epstein.
"I threw Jeffrey Epstein the hell out of Mar-a-Lago," Trump said in response.
Trump and Epstein socialised in the 1990s and early 2000s, but Trump has said they later had a falling out and that he barred Epstein from Mar-a-Lago, the Republican leader's private club in Palm Beach, Florida.
Trump typically accuses protesters who interrupt his rallies of being paid to do so, as they are carted off by security.
Also hitting the road was US Vice President JD Vance, who campaigned in North Carolina, where Republicans have been pessimistic about retaining a Senate seat.
Trump's public approval rating has fallen to a near record low, with Americans increasingly sour on the high cost of living and the Iran war, but he remains an animating force in the party and has campaigned hard to increase Republican turnout.
Americans have been voting for weeks, with 40 million ballots already cast, according to the University of Florida's Election Lab.
A total of 45.9 million Americans voted early in the last midterm elections in 2022.
Thirty-five of the 100 Senate seats and all 435 seats in the House of Representatives are being contested on Tuesday.
Nonpartisan analysts generally favour Democrats' chances of capturing a majority in the House, with the contest for the Senate seen as very close.
With AP
