SHANNON LISS-RIORDAN, a labor attorney who has won concessions from some of the best known corporations, earning the sobriquet “The Sledgehammer,” announced a Democratic primary challenge against US Sen. Ed Markey on Monday.

“I think that my experience as a worker’s rights lawyer, as a woman, as a mother, as a political outsider gives me a perspective that I think is what we need in Congress now,” Liss-Riordan said in a phone interview. “We don’t have enough women in Congress. We need more women in the Senate.”

The challenge, which will be decided between now and September 2020, is more evidence of the recent political energy within the Democratic party, where the current field of legitimate presidential contenders exceeds 20.

Last year, a wave of Democratic candidates not only swept the party into control of the US House – though not the Senate – it also ushered in a record number of women to the chamber and ended the careers of some entrenched Democrats who were bested by primary opponents.

So far, Markey and Liss-Riordan have pointed to their own records and backgrounds rather leveling any direct criticisms against their opponent, and the two have a fair amount in common ideologically – though there are bound to be contrasts over the next year and a half of campaigning.

Both Markey and Liss-Riordan are staunch supporters of US Sen. Elizabeth Warren’s presidential campaign. Markey endorsed Warren at her campaign kickoff, and Liss-Riordan said she is “all in” for her. Warren endorsed Markey when she launched her presidential bid.

At 72, Markey is 23 years older than Liss-Riordan, a Houston native who has lived in Massachusetts most of her life. He has been in Congress since 1976 and the US Senate since 2013, but he has tapped into the youthful energy that infused the Capitol last cycle, co-sponsoring the Green New Deal with New York Congresswoman Alexandria Ocasio-Cortez, who beat the so-called “Queens machine” in ousting a veteran Democratic congressman in last year’s primary.

In an appearance before the New England Council on Monday, Markey said the 2020 race could be a referendum on how to confront global warming.

“I’m hoping Republicans will side with us, but if they don’t I’m more than willing to have this be a showdown, because ultimately if Donald Trump gets a second term, it’s the equivalent of a death sentence for the planet,” Markey told the business leaders.

The two candidates diverged on the question of whether Congress should impeach Trump, with Markey echoing the more cautious approach endorsed by House Speaker Nancy Pelosi.

“What we need is the investigation. What we need is all of the facts to be put out on the table,” Markey said. “We need Robert Mueller to testify. We need other key witnesses to testify. We need first to establish through an investigation what exactly happened before we reach the question of impeachment. That is in fact the correct way to proceed.”

Liss-Riordan said Trump should be impeached now.

“I think President Trump should be impeached,” Liss-Riordan said. “I think he’s an embarrassment to our country. He has obstructed justice. He is a racist. He’s stonewalling investigations. He’s causing a crisis in our country, and he does not deserve the position he has now.”

So far, it seems, Markey’s approach to the challenge is to point to his record and avoid confronting his opponent or her stated reasons for running – the need for a “fresh voice” and more representation by women in Washington.

“I work as hard as I can every day on the Green New Deal, on creating jobs in the Commonwealth, fighting for a woman’s right to choose, ensuring that we have the strongest possible gun laws on the books,” Markey told reporters Monday. “Ultimately, good policy is good politics. The better you do your job, the more likely the voters will say, ‘That’s somebody that is fighting for me.’”

The Malden Democrat said he would earn votes by “running on the issues I’m fighting for every single day.”

Shortly afterwards, Markey’s campaign announced some hires. Field First, a firm led by campaign veteran Carl Nilsson, will run the senator’s organizing efforts, with Chelsie Ouellette playing a major role. Colleen Coffey and Michael Pratt will fundraise locally, while Stephanie Swain will lead the national finance team. Saul Shorr and Adam Magnus will serve as media consultants, and Seward Square Strategies, led by Jason Rosenbaum, will run online fundraising and digital media.

Liss-Riordan hasn’t yet selected a campaign manager, and the successful lawyer would not say how much of her own money she intends to put toward her run.

In 1991, the Senate Judiciary Committee’s conduct investigating the sexual harassment claims Anita Hill made against Clarence Thomas before his confirmation to a seat on the US Supreme Court inspired Liss-Riordan to become an activist. Nearly three decades later, the same committee’s inquiry into sexual assault accusations leveled against Brett Kavanaugh before his confirmation to the same court last year played into her decision to run for Senate, she said.

For the past 20 years, Liss-Riordan has been a labor attorney, taking on blue chip companies, including Starbucks, Uber, and Federal Express, among others, on behalf of workers.

Without changes in federal law, she said, the scales will tip against workers.

“The voice of working people is not being heard enough in Washington,” Liss-Riordan said. “I’m very concerned that if we don’t make a change now that the workplace as we know it, employment as we know it in this country will not exist in the coming decades. I’ve been seeing in the trenches what companies are doing now to try to sidestep all labor protections.”