Former President Barack Obama planned to retire from the campaign trail after leaving office, but President Donald Trump‘s election, and subsequent leadership in his first term, has prompted Obama to reverse course and hit the road on behalf of Democratic nominee, and his former Vice President, Joe Biden.

“Former presidents tend not to delve too deeply into politics and certainly not the politics of their successors,” David Axelrod, a former adviser to Obama, told CNN. “I think that was his plan, but Trump changed that plan.”

Obama made his first in-person appearance for the Biden campaign on Wednesday in Philadelphia.

“I loving coming to Pennsylvania,” he told the crowd, who cheered and honked their car horns in support. “You guys delivered for me twice, and I am back here tonight to ask you to deliver the White House for Joe Biden and Kamala Harris.”

While Obama had largely refrained from criticizing Trump, following a long precedent of not speaking ill of one’s successors, he has shifted course in recent weeks.

“Tweeting at the television doesn’t fix things,” Obama said in Philadelphia. “Making stuff up doesn’t make people’s lives better. You’ve got to have a plan, you’ve got to put in the work.”

He added: “We literally left this White House a pandemic playbook that would have shown them how to respond before the virus reached our shores. They probably used it to, I don’t know, prop up a wobbly table somewhere.”

Obama made another campaign stop in Miami on Saturday.

“Let me say I’ve run for president, Miami, so I just want you to know it’s a good idea to have an answer to this question,” Obama said, referencing Trump’s 60 Minutes interview in which he was reportedly asked what his priority if re-elected would be. “It’s a good idea if you’re running for re-election to say, ‘here’s what I want to accomplish.’ What did Trump say? He got mad and walked out of the interview.”

In the lead-up to Election Day, Obama is focused intently on boosting enthusiasm among black men, the Latino community and younger voters in key swing states.

He has also begun working to support competitive Senate races, appearing in four separate television ads for candidates in Maine and Michigan, South Carolina and Georgia.

“Make sure if Joe Biden wins,” Obama said in one ad, “he’ll have a Senate ready to work with them to move our country forward.”