Senator Tammy Baldwin during a news conference on Capitol Hill on March 14, 2017 in Washington, DC. (Justin Sullivan/Getty Images)

Republican voters have picked an anti-LGBT candidate to challenge the only out US Senator, Tammy Baldwin.

Baldwin, the junior United States Senator from Wisconsin, is the only openly gay politician to sit in the US Senate.

However the Democratic firebrand, who co-chairs the Congressional LGBT Equality Caucus, will face an anti-LGBT challenger in November.

Republicans picked State Senator Leah Vukmir to challenge Baldwin in this week’s primary.

The Human Rights Campaign notes that Vukmir “has repeatedly taken extreme positions far outside the mainstream”, and has derailed efforts to pass commonsense protections for LGBT+ people in the state, including protections for LGBT+ youth facing discrimination and bullying at school.

Vukmir has ties to anti-LGBT lobbying groups including the Family Research Council, and has consistently pushed for ‘freedom to discriminate’ exemptions.

Annise Parker of the LGBTQ Victory Fund said: “Wisconsin voters will have a stark choice come November – reelect Senator Tammy Baldwin, the first openly LGBTQ U.S. Senator, or elect an extremist anti-LGBTQ politician who prides herself on the divisiveness that makes Congress so unpopular.

“Leah Vukmir built her career on opposing basic equality for LGBTQ Americans and considers designated hate groups among her closest supporters.

“Wisconsin voters have a proud history of electing and reelecting groundbreaking LGBTQ candidates like Senator Baldwin, and we are confident they will reject Vukmir’s hostile agenda come November.”

Parker added: “Senator Baldwin’s reelection is considered critical to building a pro-equality majority in the U.S. Senate next year – but more importantly it is about who is on the side of average Wisconsinites.

“Leah Vukmir not only opposes equality for all Americans, she continues to put her corporate special interests ahead of the hardworking Wisconsin families Senator Baldwin champions. The choice is clear for voters come November.”

HRC Wisconsin State Director Wendy Strout said: “The choice for fair-minded Wisconsinites couldn’t be clearer this November.

“We can either support pro-equality champions like Senator Tammy Baldwin, who have spent their careers fighting to ensure that every Wisconsinite can live a life free from discrimination and harassment, or side with anti-equality candidates like Leah Vukmir who, time and time again, has worked to undermine equality for the LGBTQ community.”

HRC added: “HRC is proud to support Senator Baldwin for re-election. She is the first openly LGBTQ U.S. Senator and the first woman elected to the Senate from Wisconsin.

“Throughout her public service, she has been a pioneer for equality as a leader in the repeal of ‘Don’t Ask, Don’t Tell,’ a champion for federal hate crimes protections, and a primary sponsor of the Equality Act.

“In addition to Baldwin’s strong civil rights record, she has been a voice for Wisconsin’s working people, leading the fight for quality, affordable health care access and an economy that works for everyone.”