He defeats Trump-backed Rep. Jody Hice in the secretary of state race.
May ends with another round of notable primary elections on Tuesday, this time in Alabama, Arkansas, Georgia and Texas.
The most-watched races will be in Georgia, with primaries for governor and the Senate.
“This is a devastating tragedy,” Cisneros wrote on Twitter. “How many more mass shootings do children have to experience before we say enough? Sending my condolences to the children and families in Uvalde who are experiencing this unthinkable tragedy.”
Cuellar said he was “heartbroken” and urged the public to come together to support the community.
Stacey Abrams, a Black Democrat running for Georgia governor, declined on Tuesday to directly comment on Republican David Perdue saying she should "go back to where she came from."
"No, not at all," Abrams, said at a news conference in Atlanta, when asked by ABC News whether she wanted to respond to what was widely labeled as racist remarks from Perdue on Monday night while giving a campaign speech in which he also charged she was "demeaning her own race."
"I will say this," Abrams told ABC News at Tuesday's press conference. "I have listened to Republicans for the last six months attack me. But they've done nothing to attack the challenges facing Georgia. They've done nothing to articulate their plans for the future of Georgia. Their response to a comment on their record is to deflect and to pretend that they've done good for the people of Georgia."
Perdue, running to get the GOP nomination for Georgia governor, seized on Abram's comments last week that Georgia was "worst state in the country to live," citing residents' disparities in mental health and maternal mortality, among other issues.
"She ain't from here. Let her go back to where she came from," Perdue, a former senator challenging Gov. Brian Kemp for their party's nomination, said at a campaign event in the Atlanta suburbs on Monday night. "She doesn't like it here."
A historic number of people have voted early in Georgia’s primary elections. According to the secretary of state’s office, approximately 857,401 people voted in-person or through an absentee ballot as of Friday -- roughly three times as many as at the same point in the 2018 midterm election cycle.
Republicans are touting increased voter turnout as proof a controversial election law signed last year wasn’t as restrictive as its opponents described, while Democrats say the numbers are indicative of public pushback to the legislation.
“I think it tells us that Georgia voters got the message and the message was, ‘We gotta go vote, and we've got to go vote early, and we've got to go vote in person,’” Bee Nguyen, the leading Democratic candidate for secretary of state, told ABC News’ MaryAlice Parks.
Here’s what time polls close in each state on Tuesday. All times Eastern.
Georgia: 7 p.m.
Alabama: 8 p.m.
Texas: 8 p.m. in most of the state, 9 p.m. in the western tip
Arkansas: 8:30 p.m.
Minnesota: 9 p.m
