Most of them are handwritten -- on pages ripped out of notebooks, work stationary and handmade postcards. Sometimes, they're no more than a few words scrawled on a Post-It note, stuck on a check or some cash.

Doris-Pierce, Warren's constituency outreach director, sorts through the notes, dividing them into piles. Some are strategy suggestions that get passed onto the policy team; others are personal stories or words of encouragement; some write to ask how they can volunteer with Warren's presidential campaign. Many of them end up on the "Letters to EW" wall in the middle of the senator's sprawling headquarters.

During CNN's recent visit there, Doris-Pierce chuckled as she examined an unusual kind of mail that had come in that day.

"It's a birth announcement. The baby's name is Elizabeth and it says: 'Child named after our future president,'" she said. "This one is definitely making the wall."

Almost half a year into her presidential campaign, Warren has been rising in the polls, joining her progressive rival Sen. Bernie Sanders in second place. Warren's advisers point to their focus on grassroots organizing and policy proposals -- by the campaign's count, she has released 23 already this year -- as key to their momentum.

The wall of letters, located next to Warren's organizing and political teams, offers some clues about which of the senator's decisions and ideas have resonated with voters, and helps trace some of the major milestones of her campaign so far.

"First candidate to push impeach. You go girl."

There are, for example, numerous letters written after Warren's call for the House to begin impeachment proceedings against President Donald Trump. Warren's announcement in April -- coming immediately after the release of a redacted version of special counsel Robert Mueller's Russia report -- made her the first 2020 Democratic hopeful to publicly take this stance. Others soon followed.

"Because you had the integrity to say, after reading the Mueller Report, that Congress should start an impeachment proceeding now I am sending your campaign a contribution of $100," read a typed note. The man, Roger, signed his name in blue ink under the words "thank you."

Diana and Robert, a retired couple still undecided on which candidate to ultimately support, wrote that they "just happen to think you are so right about 'doing the right thing' to start the impeachment process." But accompanying their check -- what they said was their first donation this election -- was also an apology.

"Sorry I had to post-date the check," they wrote. "Our income doesn't get in until then."

"President Warren. Behind you all the way," Lynn Misheff wrote on Kent State University Alumni Association stationary. "First candidate to push impeach. You go girl." It was dated April 25 -- six days after Warren's call for impeachment proceedings into Trump.

Reached by phone, Misheff told CNN that Warren's push to begin impeachment proceedings was what prompted her to donate $35 to the senator's campaign in April.

"I was on my way to the grocery store but that's what made me take the time and get it in the mail, my check," she said. "I'd been following her and it was time to put the money behind it. The day before she talked about impeachment and the next day I said: 'I've got to get this (check) out."

But Misheff, 68, a social worker who voted for Hillary Clinton in 2016, isn't so sure yet that the 2020 race will shake out with Warren on top.

"It's probably going to be (Joe) Biden unless he really slips up bad because he's going to be the one that can beat Trump," she said. "I thought we were ready for a female president when Hillary ran. But I don't think the country was."

"Love your plans"

Warren's decision in May to reject a town hall invitation from Fox News also appears to have struck a nerve. The Massachusetts senator said she would not support Fox News' "hate-for-profit" business model by joining their town hall, as she condemned the network for balancing "a mix of bigotry, racism, and outright lies with enough legit journalism to make the claim to advertisers that it's a reputable news outlet."

A supporter named Sharon wrote a thank you note on May 16 -- two days after Warren's announcement about Fox News -- and lamented that she worried other members of Congress are "very much in the pockets of corporations."

According to the campaign, they also saw an uptick in letters as Warren's "I have a plan" slogan began to catch on, as well as following her announcement in February that she would not hold closed-door, high-dollar fundraisers during the primaries. These days, the campaign says they receive as many as 200 pieces of mail per week.

As Warren and her campaign have embraced the narrative that she is the "ideas candidate" in the crowded Democratic field, the letters on the wall feature plenty of voters that say they are craving detailed policy.

In May, one person named Lynne wrote: "Dear Senator Warren, Love your plans. Here's what I'm for." A 10-point-bullet list followed, including everything from campaign finance reform to requirements for presidents and presidential candidates to disclose their tax returns and automatic voter registration.

"Keep them coming," another note read. "More anti-trust, break-up of monopolies, duopolies, etc., livable wage, health care for all, minimum corporate tax, jail times for crooked corporate leaders..."

The coming months will show whether Warren can continue to maintain her political momentum -- and if her rise in the polls will translate to fundraising. In the first quarter, Warren raised $6 million -- a fraction of the more than $18 million haul from Sanders, who has also sworn off big-donor fundraisers. Frontrunner Joe Biden indicated this week that his campaign has already raised close to $20 million.

The Warren campaign maintains that the letters that arrive at their headquarters will continue to be one of multiple ways in which they take the pulse of voters.

On the wall, there is even a note directed at Doris-Pierce. It is addressed to: "Dear whoever opens the mail."

The person had included a check, and a request to pass along an idea to the "higher ups" on the campaign. They asked that Warren consider supporting a constitutional amendment that would make the United States Attorney General an elected official, to ensure that the person in that role is independent of the President of the United States.