Kamala Harris to appear with running mate at rally in Philadelphia on Tuesday

Kamala Harris will stage her first campaign rally with her as-yet-unnamed presidential running mate in Philadelphia next Tuesday, a decision that did nothing to dampen speculation that Josh Shapiro, the governor of Pennsylvania, is poised to join the Democratic ticket.

Late on Tuesday, the Harris campaign told Politico the first rally featuring the current vice-president and her own pick for VP would take place on 6 August, noting that an unnamed Harris aide “cautioned against reading too much into the first city chosen for the tour”.

Pennsylvania is the swing state that offers the most electoral votes , and Shapiro is a very popular figure there.

Two other governors – Tim Walz of Minnesota and Andy Beshear of Kentucky – remain under serious consideration. The US senator Mark Kelly of Arizona and Pete Buttigieg, the transportation secretary, are reportedly on Harris’s shortlist, too.

Major Democratic donors reportedly believe that Harris is set to pick a governor, a belief fueled in part by a federal rule that bars certain Wall Street employees giving to tickets featuring state officials.

Related: Who does Kamala Harris have to win over to win Michigan?

According to Axios , the Securities and Exchange Commission (SEC) rule in question is meant to “snuff out ‘pay-to-play’ schemes, where donors in the investing industry might seek to curry favor with the state officials who control the billions of dollars in state pension funds”.

The Harris campaign, the site said, has cited the SEC rule while “pressing Wall Street donors to cut their checks as soon as possible”, leading some donors, eyeing a deadline under the rule, to “think they have until Sunday to get contributions in”.

That timescale matches one floated by Gretchen Whitmer, the Michigan governor formerly touted as a running mate and who is now a Harris co-campaign chair, who said on Monday a vice-presidential pick would be named within “six or seven days”.

According to Politico, Harris and the as-yet-unnamed Democrat will go on to “barnstorm cities in seven swing states in four days”. The other rally venues named were Detroit; Raleigh, North Carolina; Savannah, Georgia; Phoenix, Arizona; Las Vegas; and western Wisconsin.

In the short time since Joe Biden conceded to Democratic demands and withdrew from his re-election campaign, Harris has dramatically reshaped the race, attracting $200m in fundraising and a rush of volunteer recruitment and leading to some encouraging polls.

On Tuesday, Bloomberg News and Morning Consult said Harris had “wiped out” Trump’s lead “across seven battleground states, as the vice president rides a wave of enthusiasm among young, Black and Hispanic voters”. Harris led by 11 points in Michigan and by two points in Wisconsin, Nevada and Arizona. Level with Trump in Georgia, she was behind in North Carolina (two points) and Pennsylvania (four).

In his first term as governor – having beaten a pro-Trump rightwing extremist, Doug Mastriano, in 2022 – Shapiro maintains strong approval ratings , even with some Republican voters. Like Harris, who is playing up her past as a prosecutor in contrast to Trump’s 34 felony convictions and 54 other criminal charges, Shapiro is a former state attorney general. At 51, he would also present a stark contrast in age and vigor to Trump, who is 78 – though not in comparison with Vance, the hardline Ohio senator and Trump running mate, who is 39.

Aides to Harris continue to seek to tamp down speculation about her running mate pick, though on Wednesday the oddstrader.com betting site gave Shapiro an “implied win probability” of slightly more than 42%, 11 points clear of the field.