In an historic first, lesbian Rep. Tammy Baldwin won her race for the U.S. Senate from Wisconsin Tuesday night, becoming the first openly gay person to serve in the Senate.

With 99 percent of precincts reporting Wednesday morning, Baldwin was ahead of former Wisconsin Gov. Tommy Thompson by a 51 percent to 46 percent margin.

“I am honored and humbled and grateful,” Baldwin said in election night remarks.  “And I am ready to get to work, ready to stand with President Barack Obama, ready to fight for Wisconsin’s middle class!”

LGBT organizations throughout the country hailed Baldwin’s victory as an important milestone in the LGBT rights movement.

“This is a historic victory not only for the people of Wisconsin, but for lesbian, gay, bisexual and transgender Americans across the country who have finally gained an authentic and powerful voice in Congress’ upper chamber,” said Chuck Wolf, president and CEO of the Gay and Lesbian Victory Fund, which provided financial  support for Baldwin’s campaign.

“Tonight Tammy shattered a glass ceiling that has existed for more than two centuries, and we could not be more thrilled,” Wolf said.

Baldwin’s supporters in Wisconsin noted that she also broke another barrier by becoming the first woman to be elected to the U.S. Senate from Wisconsin.

Chad Griffin, president of the Human Rights Campaign, which also provided financial support and field workers to assist Baldwin’s campaign, said Baldwin succeeded in drawing support from voters on a wide range of issues.

“With a relentless focus on the issues that matter to most Wisconsin voters – economic security, access to healthcare and fairness and inclusion for all,” Griffin said, “she’s earned the respect of all her constituents, gay and straight.”

As of Wednesday afternoon, the election division of the Wisconsin Government Accountability Board, which runs the state’s elections, reported that Baldwin received 1,533,868 votes, or 51 percent of the total. The board reported that Thompson received 1,370,664 votes, at 46 percent.

Two other candidates received a combined total of 3 percent of the vote, the board reported.

Early polls showed Thompson with a slight lead over Baldwin shortly after Thompson won the GOP nomination in a primary in August. By the middle of September, polls showed Baldwin in the lead, but the size of her lead narrowed by late October, with some pollsters saying the two candidates were in a statistical tie going into Tuesday’s election.

Baldwin’s quest to become the nation’s first openly gay U.S. senator captured the attention of the LGBT people across the country, many of whom contributed money to Baldwin’s campaign.

She also received backing from the Democratic Senatorial Campaign Committee and other Democratic leaning groups, including labor unions, environmental organizations and the women’s advocacy group Emily’s List.

In 1998, Baldwin became the first openly gay non-incumbent to win election to the U.S. House when she won her race for Wisconsin’s Second Congressional District in which the state capital of Madison is located.

In her seven terms in Congress, Baldwin became known as one of the strongest advocates of LGBT rights in the House as well as one of the strongest champions of progressive causes and policies.

Thompson, whose supporters describe him as a moderate, served as governor of Wisconsin between 1987 and 2001. He served as Secretary of the U.S. Department of Health and Human Services in the Bush administration from 2001 to 2005. He became a candidate for the Republican presidential nomination in 2008 but dropped out of the race before the start of the primaries.

Thompson has said he personally opposes same-sex marriage and supports the Defense of Marriage Act, which defines marriage under federal law as a union only between a man and a woman. But he has said he doesn’t favor a constitutional amendment to ban marriage equality and favors leaving same-sex marriage decisions to the states.

He has said he opposes workplace discrimination based on someone’s sexual orientation but has not said whether he would support federal legislation to ban anti-LGBT discrimination in the workplace.

Although Wisconsin members of the gay Republican group Log Cabin Republicans supported Thompson, the national Log Cabin organization, which endorsed GOP presidential candidate Mitt Romney for president, didn’t endorse Thompson.

“We endorsed candidates that engaged with us and asked for our endorsement,” said Log Cabin president R. Clarke Cooper, who noted that the group endorsed just four U.S. Senate candidates this year.

The outcome of Tuesday’s Senate election in Wisconsin marked the end of a bruising campaign, which the Milwaukee Journal Sentinel says may have broken a national record for the most negative TV ads of any U.S. Senate campaign in the state and possibly in the nation.

The Journal Sentinel reports that both Baldwin and Thompson appear to have lashed out at each other with equal force, with some independent observers saying some of the ads from both sides included misleading information.

None of the Thompson attack ads appear to have singled out Baldwin based on her sexual orientation.

However, in at least one instance, a Thompson campaign official sent an email to the news media in early September, one day before Baldwin spoke before the Democratic National Convention in Charlotte, N.C., highlighting Baldwin’s appearance at an LGBT Pride festival in Madison several years earlier.

The email, sent by Thompson campaign staffer Brian Nemoir, included an attached YouTube video showing Baldwin waiving her arms while dancing on a stage with the popular Wisconsin rock band V05. Some of the band members were dressed in Wonder Woman costumes as the band played the theme song for the Wonder Woman TV series.

Nemoir stated in his email that Baldwin was scheduled to discuss “heartland values” in her Democratic Convention speech.

“Clearly, there’s no one better positioned to talk ‘heartland values’ than Tammy,” he said sarcastically in the email.

Baldwin supporters called the email a form of gay baiting, saying it was an attempt to question Baldwin’s values because she appeared at an LGBT Pride event. A Thompson campaign spokesperson said Nemoir was acting as an individual and not on behalf of the campaign when he sent the email and video.

While the Thompson campaign’s negative TV ads steered clear of Baldwin’s sexual orientation, they sought to portray her as an ultra liberal politician out of touch with the needs of the state and the country.

One ad pointed to Baldwin’s longstanding support for a single payer health insurance system, quoting her as saying several years ago that the single payer system she supported is a “government takeover of medicine.” Another ad noted that Baldwin voted four times against economic sanctions for Iran, criticizing her judgment on a key foreign policy issue.

Baldwin responded to the health insurance attack by saying she voted for and continues to support the Affordable Care Act, President Obama’s health insurance reform measure that Congress passed two years ago. She said her support for a single payer system was “moot” since the Obama measure is about to be implemented.

She said she voted against sanctions for Iran at a time when she was hopeful that dissident groups in Iran would overturn Iran’s government and establish a true democratic system. She said she began voting for sanctions after determining that the opposition forces didn’t have the strength to change the government.

A Thompson campaign attack ad that drew expressions of outrage from Baldwin’s campaign and its supporters showed video footage of the devastation of the World Trade Center in New York following the Sept. 11, 2001 terrorist attacks and denounced Baldwin for voting against a 2006 House resolution honoring victims of the attacks.

Baldwin said she voted for at least four other 9/11 resolutions honoring victims of the terrorist attacks but voted against the 2006 resolution because it included other provisions on unrelated issues with which she disagreed.

In her own TV ads, Baldwin fired back at Thompson, citing reports by New York firefighters saying the U.S. Department of Health and Human Services, which Thompson headed at the time of the 9/11 attacks, was slow in responding to firefighters’ calls for assistance for their illnesses believed to be caused by the fumes and contaminated dust that engulfed them while responding to the World Trade Center disaster.