On Feb. 1, Alaska Sen. Lisa Murkowski and Maine Sen. Susan Collins gave back-to-back speeches on the Senate floor stating their intention to vote against the confirmation of Betsy DeVos as secretary of education. This was a big deal: If one more Republican came out against Trump’s nominee, DeVos would be voted down, unless a Democrat also broke ranks. That’s when the faxes really started to pour into Pennsylvania Sen. Pat Toomey’s Washington office. He’d already been averaging a few hundred a day ever since President Trump was inaugurated; that afternoon, the number shot up to more than 300 an hour.

Those numbers come from the freemium online faxing service FaxZero, which for the last five years has been collecting and sharing the fax numbers of members of Congress and tracking data on which senators and representatives are faxed most. FaxZero’s database doesn’t include faxes sent from other online services — there’s eFax, HelloFax, even FaxCongress — nor does it include faxes sent from, well, real fax machines. And, of course, it doesn’t tell us anything about how many letters and emails are being sent, or how many phone calls are being made, or how many notes tied to rocks are being thrown through Congressional windows. But the FaxZero data does give us insight into which elected officials are being targeted more than others. And according to the company’s database, since Jan. 4, the first full day of the 115th Congress, Toomey has received more than 20,000 faxes, twice as many as Senate Majority leader Mitch McConnell and more than six times as many as any other member of Congress.

CONGRESS MEMBER PARTY STATE OR DISTRICT FAXES RECEIVED Sen. Pat Toomey R PA 21,601 Sen. Mitch McConnell R KY 9,407 Sen. John Cornyn R TX 3,228 Sen. John McCain R AZ 2,717 Sen. Dianne Feinstein D CA 2,693 Sen. Thom Tillis R NC 2,315 Sen. Jeff Flake R AZ 2,101 Sen. Cory Gardner R CO 1,952 Sen. Marco Rubio R FL 1,817 Rep. Paul Ryan R WI-1 1,813 Sen. Dean Heller R NV 1,697 Sen. Robert Casey D PA 1,568 Sen. Ted Cruz R TX 1,486 Sen. Susan Collins R ME 1,429 Sen. Lisa Murkowski R AK 1,370 Sen. Richard Burr R NC 1,370 Sen. Deb Fischer R NE 1,318 Sen. Ron Johnson R WI 1,205 Sen. Johnny Isakson R GA 1,190 Sen. Charles Schumer D NY 1,057 Sen. Kamala Harris D CA 934 Sen. Lamar Alexander R TN 882 Sen. Jerry Moran R KS 874 Sen. Lindsey Graham R SC 821 Sen. David Perdue R GA 803 Members of Congress who have received the most FaxZero faxes From Jan. 4 through Feb. 13. Source: FaxZero

The reason for Toomey’s impressive lead? A perfect storm of demographics, frustration and coordination. Pennsylvania barely went for Trump in the general election, which suggests that Toomey might be able to occasionally break with his fellow Republicans without hurting his chances of re-election. Thanks in part to the closeness of the presidential election in his state, Toomey has the lowest predicted “Trump score” — a measure of how often a member is expected to vote in accordance with Trump’s position — of any Senate Republican except Collins, Nevada’s Dean Heller and Colorado’s Cory Gardner. Those senators are also getting faxed a lot, but they have smaller constituent bases. Toomey also squeaked out a victory in his own 2016 Senate race by running as a moderate and touting Obama’s kind words about his views on gun control in ads, so his more liberal constituents have some reason to believe they can make their voices heard — and perhaps influence his vote.

One of those constituents is Hannah Laurison, an organizer with Philly UP, a political advocacy group that uses a popular online document called “Indivisible: A Practical Guide for Resisting the Trump Agenda” as a framework for coordinating progressive messages, often by mobilizing constituents to make issue-driven phone calls to Toomey’s office. “We started getting a lot of feedback that people weren’t getting through to staff, that voicemails were constantly full and that lines were busy,” she told me. As a result, the group started including the FaxZero contact information for Toomey as part of its efforts. And they weren’t the only ones; instructions to fax Toomey showed up on dozens of other local Facebook groups and the progressive site Daily Kos. Activists have held similar “fax parties” for other representatives and senators, including McConnell and Speaker of the House Paul Ryan.

Toomey’s communications director, E.R. Anderson, acknowledged in an email that the senator’s voicemail boxes occasionally fill up, but said it’s hard to quickly process all the messages coming in on various platforms due to the huge volume the office is getting each day. “There’s a lot going on in Washington now,” she said.

According to Sarah Dohl, a former communications director for Texas congressman Lloyd Doggett and a contributor to the “Indivisible” guide, faxes are less effective than in-person visits or phone calls in terms of influencing representatives, but perhaps better than form emails. And the influence faxes have may depend on what kind of fax machine the representative uses. Old-school fax machines that print out each message may have more impact because they are more likely to be treated as letters, with each one getting a personal look and a reply from a staffer, which means they get logged into the constituent-reply system. Newer fax machines turn messages into electronic letters that can be replied to with a form letter and may not be logged at all. “Faxes are all treated a bit differently in different offices,” Dohl said.

Toomey’s office uses a newer model that turns faxes into digital files, but Anderson said the staff treats them like letters, meaning that each one gets its own response in the mail. So far, though, the overwhelming number of faxes doesn’t seem to have made much of a difference. Toomey not only voted to confirm DeVos, he’s also supported Trump’s position on every relevant vote so far.