When Bernie Sanders’ Senior Advi­sor Tad Devine announced in August that the Demo­c­ra­t­ic pres­i­den­tial can­di­date would not be run­ning any attack ads against Hillary Clin­ton, many saw the move as sim­ply being con­sis­tent with his pre­vi­ous cam­paign strate­gies and his pro­gres­sive plat­form. Sanders has said he ​“hates and detests these 30-sec­ond neg­a­tive ads” and has nev­er run one. He sees the ads as part of what’s bro­ken with Amer­i­can pol­i­tics, and his dis­avow­al of them fits with his elec­toral reform poli­cies, which con­demn super PACs and the buy­ing and sen­sa­tion­al­iz­ing of U.S. elections.

If Clinton ran an attack ad, she risked coming off as desperate or a bully. But by not running attack ads, she would essentially render herself unable to combat any surge in the polls by Sanders.

But Sanders’ refusal to pro­duce attack ads has proven to be more than a mat­ter of sim­ple moral con­sis­ten­cy. His pledge rep­re­sent­ed a shrewd polit­i­cal deci­sion by the Sanders cam­paign — a deci­sion that has now paid off.

Elec­toral reform is cen­tral to Sanders’ plat­form for pres­i­dent. By swear­ing off attack ads against his oppo­nents and cash from super PACs which often fund such ads, he has attempt­ed to show that unlike his oppo­nents, he can actu­al­ly car­ry out the ideals he speaks so often about. In fact, short­ly after Bernie’s announce­ment, his cam­paign sent a cease-and-desist let­ter to a PAC sup­port­ing him, which was first formed by Con­gres­sion­al lob­by­ist Cary Lee Peter­son to encour­age the Ver­mont Sen­a­tor to run.

Mean­while, Clin­ton, who earned a rep­u­ta­tion for cut­ting attack ads dur­ing her 2008 pres­i­den­tial bid against Oba­ma, is run­ning on a sim­i­lar­ly pro­gres­sive elec­toral reform plat­form — while also glad­ly accept­ing more than $20 mil­lion in sup­port from Pri­or­i­ties USA Action, her Super PAC. At the same time as her own web­site crit­i­cizes the Supreme Court’s Cit­i­zen Unit­ed case, say­ing it ​“helped unleash hun­dreds of mil­lions of dol­lars of secret, unac­count­able mon­ey into U.S. elec­tions that is drown­ing out the voic­es of ordi­nary Amer­i­cans and dis­tort­ing our democ­ra­cy,” Hillary is seek­ing some $2 bil­lion , much of it PAC mon­ey, for her campaign.

How­ev­er, the polit­i­cal depth of Bernie’s refusal to run neg­a­tive attack ads has proven far more impor­tant than reveal­ing con­trasts between the two can­di­dates. This deci­sion actu­al­ly forced Hillary’s cam­paign into an incred­i­bly dif­fi­cult posi­tion. If she ran an attack ad, she risked com­ing off as des­per­ate or a bul­ly. But by not run­ning attack ads, she would essen­tial­ly ren­der her­self unable to com­bat any surge in the polls by Sanders.

Until recent­ly, Clin­ton had held off on run­ning neg­a­tive pub­lic­i­ty. But Sanders’ self-iden­ti­fi­ca­tion as a social­ist must have been too hard for her cam­paign to resist attacking.

On Sep­tem­ber 14, the Huff­in­g­ton Post received an email from one of Clinton’s Super PACs that inti­mat­ed Sanders would begin diplo­mat­ic ties with ter­ror­ists and linked him to the social­ist for­mer Pres­i­dent of Venezuela, Hugo Chavez. In its report on the email, Huff­Post con­clud­ed it was unclear whether the mes­sage would be dis­sem­i­nat­ed to any­one else. If it was, how­ev­er, ​“the attack would be in the vein of what Sen. Claire McCaskill (D‑Mo.) said about Sanders ear­li­er this year — that he’s une­lec­table, since he’s a self-iden­ti­fied demo­c­ra­t­ic socialist.”

Sanders’ cam­paign was quick to react to this attack, send­ing out an email that illus­trat­ed the dif­fer­ence between his polit­i­cal strat­e­gy and that of the ​“bil­lion­aire class.” ​“Let’s send a pow­er­ful mes­sage that we have had ENOUGH of the bil­lion­aire class buy­ing elec­tions,” the email read. ​“If we stand togeth­er to fight back against these ugly attacks, we can ensure this elec­tion is about who has the best ideas, and not who has the biggest donors.”

With­in two days, the Sanders cam­paign had raised $1.2 mil­lion in grass­roots con­tri­bu­tions. Accord­ing to the exec­u­tive direc­tor of Act­Blue, the pro­gres­sive fundrais­ing web­site Bernie uses to receive online dona­tions, at one point dur­ing the blitz, they were receiv­ing 180 con­tri­bu­tions per minute.

And on Sep­tem­ber 20, less than one week after the Super PAC attack first went live, Hillary promised CBS News’ John Dick­er­son on ​“Face the Nation” that she has ​“no inter­est” in run­ning attack ads on Bernie. ​“I want this to be about ideas and about poli­cies,” she said. ​“I know Bernie. I respect his enthu­si­as­tic and intense advo­ca­cy of his ideas. That’s what I want this cam­paign to be about, and I hope peo­ple who sup­port me respect that.”

In fact, this was one of the first times since his announce­ment that Sanders was explic­it­ly men­tioned by Clin­ton. In the past, she has avoid­ed say­ing his name and declined to com­ment on the threat his cam­paign pos­es to her suc­cess in the primaries.

Sanders’ com­mit­ment to refrain from pro­duc­ing attack ads paid off, allow­ing him to illus­trate a vital con­trast between him­self and Clin­ton — and rais­ing his cam­paign more than a mil­lion dol­lars in dona­tions in the process. Fur­ther­more, his con­sis­ten­cy forced Clin­ton to back­track on an impor­tant issue under pub­lic scruti­ny, rein­forc­ing the notion that she is sim­ply a politi­cian will­ing to do what­ev­er it takes to win while Sanders oper­ates out of an iron­clad com­mit­ment his pro­gres­sive ideals.

Such com­mit­ment is a big part of why Sanders’ cam­paign has proven so refresh­ing for so many Amer­i­can vot­ers, and for mil­len­ni­als in par­tic­u­lar. This gen­er­a­tion has large­ly been dis­il­lu­sioned with U.S. pol­i­tics: Few­er mil­len­ni­als vote , join polit­i­cal par­ties or con­sid­er pol­i­tics one of their inter­ests than in pre­vi­ous gen­er­a­tions. But Sanders’ cam­paign has rein­vig­o­rat­ed a large pro­por­tion of the country’s newest vot­ers: some 59 per­cent of col­lege-aged Democ­rats sup­port Sanders, com­pared to Clinton’s 18 per­cent, a Chegg Media Cen­ter poll reports. Almost half of the stu­dents sur­veyed find Hillary ​“unfa­vor­able.”

Sanders has man­aged to pull Clin­ton to the left on yet anoth­er issue. As he con­tin­ues to surge in the polls, Clin­ton is respond­ing by mov­ing left on issues as diverse as Black Lives Mat­ter, the Key­stone XL pipeline, Wall Street and elec­toral reform and even the Fight for 15. As long as Sanders con­tin­ues to main­tain his pro­gres­sive stances on a num­ber of oth­er issues, his prin­ci­pled cam­paign­ing will like­ly con­tin­ue to trans­late into tan­gi­ble polit­i­cal gains.

By the end of the pri­maries, regard­less of who wins, the can­di­date will either be a true pro­gres­sive ded­i­cat­ed to com­bat­ting inequal­i­ty, fight­ing sys­temic racism, and run­ning a clean cam­paign, or some­one forced to cham­pi­on a num­ber of pro­gres­sive caus­es that she like­ly would have bare­ly con­sid­ered oth­er­wise. And, unlike Hillary Clin­ton, that’s what mat­ters to Bernie Sanders — that some­one, any­one, gets the job done.