Former interim Democratic National Committee chairwoman Donna Brazile made waves with allegations that the party’s 2016 presidential primary was tilted against Sen. Bernie Sanders (I., Vt.), and Sanders responded Monday with a message to his supporters.

Sanders prioritized potential changes in the Democratic Party, such as reducing the number of superdelegates, making primaries and caucuses more accessible, and providing greater transparency to party decisions, the Burlington Free Press reports. The senator addressed Brazile’s book by arguing the party needs to fix its systemic problems in order to defeat Republicans.

"What the recently released book excerpt from former interim DNC Chair Donna Brazile made clear is that unless we get our act together, we are not going to be effective in either taking on Donald Trump or in stopping the extremist right-wing Republican agenda," Sanders wrote.

Brazile alleged that a joint fundraising agreement between the DNC and Hillary Clinton campaign gave Clinton influence and control over finances that other Democratic candidates did not have. Brazile, however, has backtracked about whether the primary was "rigged" in Clinton's favor. Sanders said a fairer process would better reflect the will of voters.

"We have to re-establish faith with the American people that in fact we can make positive changes in this country through a fair and transparent political process that reflects the will of voters across this country," he said.

Sanders has remained focused on reforming the party and defeating Republicans even as word has come out that the DNC tilted the primary against him. Brazile wrote in her book that Sanders reacted to the news "stoically" when she told him privately last year, and he has generally downplayed the controversy that has arisen since Brazile made the allegations publicly.

Last week, President Donald Trump tweeted derisively about Clinton’s control of the DNC, and Sanders responded that such talk was a distraction from policy issues.

We won't be distracted from your efforts to give billionaires tax cuts, take health care from millions and deny climate change. Do your job. https://t.co/35eWaiMuYt — Bernie Sanders (@SenSanders) November 3, 2017

Former Sanders presidential campaign manager Jeff Weaver, however, said on Friday that the nomination process was not fair and called for the DNC to apologize.

"I think the DNC should apologize to the millions and millions of people who put their heart and souls into the campaign on both sides, frankly," Weaver said on MSNBC. "There are many people out there who campaigned for Hillary thinking that it was a fair process. It was not a fair process."