Barack Obama made his first appearance on the campaign trail for Kamala Harris on Thursday, speaking at a rally in Pennsylvania and at an event for Black voters, where he urged men in particular to support the vice-president.

In comments directed specifically to Black men in the swing state during an event at one of Harris’s campaign offices, Obama questioned their unwillingness to vote for her – a September NAACP poll showed that over one quarter of Black men under 50 say they will vote for Donald Trump.

“We have not yet seen the same kinds of energy and turnout in all quarters of our neighborhoods and communities as we saw when I was running. Now, I also want to say that that seems to be more pronounced with the brothers,” Obama said.

“You’re coming up with all kinds of reasons and excuses. I’ve got a problem with that.

“Part of it makes me think that, well, you just aren’t feeling the idea of having a woman as president, and you’re coming up with other alternatives and reasons for that.”

He added: “When we get in trouble and the system isn’t working for us, they’re the ones out there marching and protesting.”

Later in the evening, at the Fitzgerald Field House in Pittsburgh, where thousands appeared to be in attendance, the Democratic party leader called on residents of the crucial swing state to vote for Harris – and down-ballot for other Democratic candidates like Pennsylvania Senator Bob Casey.

“We need a president who actually cares about solving problems and making your life better, and that’s what Kamala Harris will do,” Obama said. “And to help her do it, she will need a Senate full of serious public servants like Bob Casey.”

With 19 electoral college votes, Pennsylvania is essential for either candidate to win the election. Recent surveys released by Quinnipac University showed Harris leading in Pennsylvania, but polling between the vice-president and Donald Trump has been close.

The state may also determine control of the Senate: Casey, for example, is up for re-election and facing a well-funded Republican opponent.

Obama and Harris have long been supporters of each other’s campaigns, and at the Democratic national convention in August the former president and his wife sought to cast Harris as the heir to their movement. Harris was an early supporter of Obama’s long-shot bid against Hilary Clinton, starting in 2007 when she knocked on doors for him ahead of the Iowa caucuses. In 2010, when Harris ran for attorney general of California, Obama backed her campaign – calling her “a dear, dear friend of mine”.

In Pittsburgh on Thursday, Obama acknowledged American voters’ frustrations with inflation, the Covid recovery and other issues – while denouncing Trump and praising Harris’s platform.

“This election is going to be tight because there are a lot of Americans who are still struggling out there,” Obama said. “I get it why people are looking to shake things up. I mean, I am the hope-y, change-y guy. So I understand people feeling frustrated. We can do better. What I cannot understand is why anybody would think that Donald Trump will shake things up in a way that is good for you.

“The good news is, Kamala Harris – she doesn’t have concepts for a plan. She has an actual plan to make your life better.”

Harkening back to the message he shared with Black voters earlier in the day, Obama later added: “I’m sorry, gentlemen, I’ve noticed this, especially with some men who seem to think Trump’s behavior of bullying and putting people down is a sign of strength. And I am here to tell you: that is not what real strength is. It never has been.

“Real strength is about helping people need it and standing up for those who can’t always stand up for themselves, that is what we should want for our daughters and for our sons, and that is what I want to see a president of the United States of America.”

Before the former president took the stage, Pennsylvania governor Josh Shapiro, who was among those shortlisted to be Harris’ running mate, touted the Democratic party’s work in the state to expand universal free breakfast and gun violence prevention efforts, while criticizing Republican party leadership on the national level. He specifically encouraged attendees to vote to re-elect Casey.

Casey himself spoke, laying out the stakes for the upcoming election and denouncing his rival, David McCormick. McCormick, a businessman, ran the world’s largest hedge fund while it managed and advised funds holding hundreds of millions of dollars in Russian debt, documents obtained by the Guardian show.

“These out-of-state billionaires [are] spending more than $100m to defeat me in this race. Well, I got news for those billionaires. I’m going to beat David McCormick, and I’m going to beat those billionaires,” Casey said.

Obama’s appearance comes as Democratic surrogates are campaigning for Harris in swing states across the country. This week, the Harris campaign confirmed that vice-presidential nominee Tim Walz will campaign in Wisconsin, former president Bill Clinton will tour the southern states of Georgia and North Carolina, and Vermont senator Bernie Sanders will host events in Michigan. Meanwhile, former first lady Michelle Obama has relaunched Party at the Polls, a program of her non-partisan voting initiative When We All Vote.

At the same time, Republican vice-presidential candidate JD Vance held a town hall Thursday evening in Greensboro, North Carolina, shortly after Trump spoke in Detroit.