(NewsNation) — Michigan Gov. Gretchen Whitmer and Pennsylvania Gov. Josh Shapiro campaigned on behalf of Vice President Kamala Harris in Bucks County, Pennsylvania, on Monday.

This comes as NewsNation learns Harris has started reviewing binders of information about potential VP contenders.

Shapiro is said to be on the vice president’s short list of potential running mates. However, Whitmer withdrew herself from consideration, saying she wasn’t leaving Michigan anytime soon.

Governors Andy Beshear, D-Ky., Tim Walz, D-Minn., and Transportation Secretary Pete Buttigieg also had a busy weekend on the trail. They each headlined activities of the Harris Campaign’s Weekend of Action to ramp up voter enthusiasm now with Election Day 100 days away.

They, along with fellow Governors J.B. Pritzker, D-Ill., and Arizona Sen. Mark Kelly are hoping to get a good review from Harris. They all are somewhere on the list of contenders to be Harris’ running mate, NewsNation has been told.

Gov. Roy Cooper, D-N.C., informed Kamala Harris’ campaign he is withdrawing from consideration to be her vice presidential pick, The New York Times reported.

VP contenders under review

Harris is expected to announce her running mate before August 7^th, two sources with knowledge of the matter tell NewsNation. August 7^th is when the Democrats’ virtual nomination roll call is scheduled to be completed so the party will need to present its completed ticket.

The vice president is looking for a running mate who she believes “balances” the ticket, someone who can be a governing partner and has executive experience, according to a separate source with knowledge of the matter. Also important to her is somebody she has chemistry with, feels comfortable with and a person she feels she can trust, the source adds.

That all has meant an accelerated vetting process, which usually runs months, has to be completed in weeks.

“That process has begun in earnest and we do not expect to have additional updates until the Vice President announces who will be serving as her running mate and as the next Vice President of the United States,” a spokesperson for the campaign tells NewsNation.

A campaign official confirmed to NewsNation that the process is underway, without elaborating further on where it stands. Those under consideration have been asked to submit a range of materials — financial, biographical and political — to the team overseeing the process.

In the past week, many potential candidates have appeared at all hours of the day and night on the airwaves promoting Harris and ripping into former President Donald Trump. Others have made the case by talking to reporters or at campaign events. 

Possible Harris-Shapiro ticket

With his 61% approval rating in the king of the battlegrounds, Shapiro is among several leaders on the ground in the Keystone State, speaking to voters over the weekend and joining Harris supporters in an all-out weekend of action across battleground states to register voters.

Buck County is a purple county in the crucial swing state and currently has more than 478,000 registered voters. There’s been a recent shift in the county as more residents are registering to vote Republican rather than Democratic, the first time since 2007.

NewsNation spoke with a handful of county voters, getting their opinions on a possible Harris-Shapiro partnership.

“He’s my man, and he’s always been my man, and if he’s running, he’s got my vote. It’s not like Kamala didn’t have my vote. Now you’ve got double the vote from me,” Pennsylvania resident Gary said.

Democratic voters said they are voting left no matter what, but Harris needs to win swing votes to clinch the state during the November election. Shapiro could help her chance at winning Pennsylvania.

While NewsNation did not encounter any undecided voters on the ground in Bucks County, the team did speak with Trump supporters, who unexpectedly liked things about Shapiro.

“There’s things I like about him,” one Trump voter said. “No matter how much I might like some of the things he does, I would not vote for him.”

What about a Harris-Whitmer ticket?

Whitmer agreed to co-chair Harris’ campaign following President Joe Biden’s decision to drop out of the 2024 race.

Whitmer was among the names floated to replace Biden as the Democratic nominee, but the president and Whitmer have since endorsed Harris for the role.

While Whitmer will be campaigning on behalf of Harris, she previously told a reporter in her home state that she is “not leaving Michigan” and has no plans “to go anywhere.”

The Michigan governor is also placed in a key state for the election and recently said she was uninterested in running for president should Biden step aside.

Whitmer is in her second term and is a staunch advocate of abortion. She has publicly said she was raped during college. She has approved several gun violence prevention bills and admitted border reform is needed while acknowledging the positive impact immigration can have on the economy.

There has been speculation, though, about Whitmer emerging on a national stage beyond 2024, with some reports suggesting she could be a presidential contender in 2028.

Don’t sleep on Sen. Mark Kelly

The field in the unexpected veepstakes is far from settled, with other names certain to be floated in the coming weeks until one comes to the forefront for a party that is trying to unify, and do so quickly. 

However, while some of those in contention have been more publicly promoting Harris, Kelly has not been as active. Some Democratic consultants see him as a strong contender because of his personal story and experience as a border state senator working on those issues. 

Kelly has risen to near the top of the list of possible running mates as Harris considers whom she wants to run alongside her.

The Arizona senator was sent vetting materials as one of a handful of Democrats under consideration for the role. A veteran and former astronaut, Kelly brings a background that is unique compared to other possibilities being considered.

He also enjoys strong popularity in his purple battleground state of Arizona, one that could help decide the winner of the November election.

Democrats have expressed enthusiasm around Kelly since he first won his Senate seat in a 2020 special election to serve the remainder of the late Sen. John McCain’s, R-Ariz., term. He was then elected to a full term in the Senate in 2022. 

In both cases, he won by a few points and performed better than President Biden in the state in 2020 and now-Gov. Katie Hobbs in 2022.

What about a Harris-Walz ticket?

Minnesota Gov. Tim Walz entered the running mate chat earlier this week, with Democrats praising his affable persona, praise among unions and national experience as chair of the Democratic Governors Association. 

“I think Walz is making a strong case,” one Democratic source told NewsNation. 

It remains unknown if Walz, 60, was sent vetting material from Harris’ campaign, but he told CNN’s “State of the Union” on Sunday that “being mentioned is certainly an honor.”

Appealing to Democratic voters has also helped Walz land on the list being vetted to potentially be Harris’ running mate, especially after his comments regarding Trump and Vance earlier this week.

“These guys are just weird,” Walz said in an MSNBC interview. “They’re running for He-man women-haters club or something.”

The Hill contributed to this report.