The American Civil Liberties Union has spent nearly $1 million on mailers to voters in crucial presidential primary states highlighting leading candidates’ positions on criminal justice reform and immigration ― and pointing out that former Vice President Joe Biden has avoided taking firm stances.

More than 130,000 mailers, part of the group’s quest to spend $30 million shaping the 2020 presidential election, are set to arrive in the mailboxes of voters in South Carolina, Georgia and Michigan this week. The century-old group has already sent 650,000 mailers to voters in the early voting states of Iowa, New Hampshire, Nevada and the delegate-rich Super Tuesday states of California and Texas.

As a nonprofit, the ACLU is not allowed to officially endorse candidates. But it wants to shape the debate around civil liberties during the 2020 primaries, and has asked the major Democratic and Republican candidates — including President Donald Trump — to commit to civil libertarian issues, including cutting the federal prison population by half, ending CIA drone strikes overseas and creating a path to citizenship for undocumented immigrants.

But the Biden campaign hasn’t responded to a questionnaire the ACLU sent to the candidates. And each of the three mailers — one focused on criminal justice reform, another on immigration and a third on broader civil liberties issues — notes that Biden has declined to answer the group’s questions.

“We think voters deserve to know specifically ― not just generic, rhetorical stump speech talk ― on where you stand on these civil liberties and civil rights issues,” said Ronald Newman, the ACLU’s national political director, adding he still hopes Biden will engage with the group. “We think the failure to go on the record on these issues is concerning.”

Asked for comment, the Biden campaign pointed to its response to an earlier ACLU radio ad that pressured the former vice president to clarify his position on civil rights. In that case, the campaign highlighted a civil rights activist who questioned why the civil liberties group was inserting itself into the Democratic primary. The campaign has also committed to some of the ACLU’s positions, including a pathway to citizenship for undocumented people, in its plans for immigration and criminal justice reform.

Most of each mailer is dedicated to explaining where four other candidates – Massachusetts Sen. Elizabeth Warren, entrepreneur Andrew Yang, Vermont Sen. Bernie Sanders and former South Bend, Ind. Mayor Pete Buttigieg – stand on a variety of issues. (The ACLU used the national RealClearPolitics polling average to determine the candidates it would highlight, Newman said.)

The mailers highlight several instances in which each candidate breaks from the others. Only Warren, for example, would not pledge to reduce the number of immigrants in detention by 75%. Only Buttigieg wouldn’t pledge to end CIA drone strikes “that often kill civilians.” And only Yang wouldn’t commit to cutting the federal prison population in half.

Every candidate, including Sanders, failed to commit to decriminalizing all drug use. (Sanders’ campaign manager, Faiz Shakir, previously ran the ACLU’s political program.)

The mailers are not the first time the ACLU has taken Biden to task. In a radio advertisement in South Carolina that aired this fall, the group questioned the former vice president’s commitment to criminal justice reform.

“We asked how he would address the unnecessary use of force by police, incidents that have led to countless tragedies and created distrust of those sworn to protect us,” a narrator said in the ad. “No response. Voters deserve to know: Does Joe Biden support rights for all?”

The ACLU, which saw its fundraising and membership soar following Trump’s election in 2016, has rapidly increased its political work in recent years, getting heavily involved in referendums on civil liberties issues and playing a significant role in local district attorney races and other elections.