Female Democratic senators are privately urging Sen. Elizabeth Warren Elizabeth WarrenNo new taxes for the ultra rich — fix bad tax policy instead Democrats back away from quick reversal of Trump tax cuts It's time for newspapers to stop endorsing presidential candidates MORE to formally endorse Hillary Clinton Hillary Diane Rodham ClintonBarr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' Virginia Democrat blasts Trump's 'appalling' remark about COVID-19 deaths in 'blue states' The Hill's Campaign Report: Biden asks if public can trust vaccine from Trump ahead of Election Day | Oklahoma health officials raised red flags before Trump rally MORE for president.

The lobbying campaign comes as the Democratic race between Clinton and Sen. Bernie Sanders Bernie SandersSenate Republicans signal openness to working with Biden Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll Schumer, Sanders call for Senate panel to address election security MORE (I-Vt.) is heating up going into the New Hampshire primary next week.

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A group of Democratic ­senators is taking a bus tour of New Hampshire this weekend to stump for Clinton, and they want the liberal Massachusetts powerhouse to get on board. Clinton narrowly defeated Sanders in the Iowa caucuses earlier this week, but the Vermont senator is a heavy favorite to win New Hampshire.

A few of the senators have discussed with Warren the possibility of publicly backing Clinton. However, they’ve been careful not to put a lot of public pressure on their colleague, who is fiercely independent and has a loyal following among progressives.

“I’m hopeful she’ll join us. I’m hopeful she’ll join the revolution that will allow us to come together to elect” the first female president, said Sen. Debbie Stabenow Deborah (Debbie) Ann StabenowGAO report finds brokers offered false info on coverage for pre-existing conditions Democrats back away from quick reversal of Trump tax cuts Battle looms over Biden health care plan if Democrats win big MORE (D-Mich.), one of Clinton’s staunchest supporters.

Asked if she or other senators had approached Warren personally, Stabenow said, “We all talk about it,” but declined to reveal what Warren has said in response.

Sen. Barbara Mikulski Barbara Ann MikulskiForeign policy congressional committees need to call more women experts Lobbying World Only four Dem senators have endorsed 2020 candidates MORE (Md.), the dean of the Senate’s Democratic women, has also talked to Warren about backing Clinton.

“I’ve told Sen. Warren that we would welcome her anytime she’s ready,” she said.

Warren is the only female Democratic senator who has not endorsed Clinton.

Mikulski indicated she is not making a hard sell. She’s more focused on revving up Democratic primary voters in New Hampshire and South Carolina.

“I’m going up to New Hampshire to be on a bus tour with [Clinton] on Friday. Many of the Democratic women of the Senate are going to do that. And we’re getting ready to organize another tour in South Carolina,” she said.

Warren declined to comment in the Capitol Wednesday, and her office did not return a request for comment.

An endorsement from Warren would be very valuable now. Sanders is leading Clinton by double digits in New Hampshire, where Warren has a higher profile than in most states because it’s part of the Boston media market.

Clinton is likely to pick up the endorsement of Rep. Nancy Pelosi (D-Calif.), who was the first female Speaker. Pelosi, who is revered by progressives, told The Hill on Tuesday she will endorse in the primary, and all indications suggest she will back the former first lady.

Warren, meanwhile, has been coy.

This week, Warren told reporters, “No endorsements now.” She said she is proud that her party’s White House hopefuls are focusing on the issues voters care about. Asked if she’d endorse a candidate following the Iowa caucuses, Warren responded, “We’ll see.”

Clinton has labored to compete with Sanders for liberal activists and young voters, two blocs that helped then-Sen. Barack Obama Barack Hussein ObamaGOP senator blocks Schumer resolution aimed at Biden probe as tensions run high D-Day for Trump: September 29 Obama says making a voting plan is part of 'how to quarantine successfully' MORE (Ill.) defeat her in the 2008 presidential primary. Warren, an idealist who often takes on Wall Street interests aggressively, is popular with those voters.

A Democratic aide said the Senate women have been “trying to do a little arm twisting in recent months.”

“Her role in this campaign would be valuable,” the staffer said. “I think she’s gotten more attention than most senators, and I think it would mean a lot.”

Other women in the Senate have thrown themselves wholeheartedly into the campaign for Clinton, which they see as a historic opportunity to advance women’s rights.

Sens. Kirsten Gillibrand Kirsten GillibrandSuburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits The Hill's Campaign Report: 19 years since 9/11 | Dem rival to Marjorie Taylor Greene drops out | Collin Peterson faces fight of his career | Court delivers blow to ex-felon voting rights in Florida MORE (D-N.Y.) and Jeanne Shaheen Cynthia (Jeanne) Jeanne ShaheenSenate Democrats introduce bill to sanction Russians over Taliban bounties Trump-backed candidate wins NH GOP Senate primary to take on Shaheen Democratic senator urges Trump to respond to Russian aggression MORE (D-N.H.) said they would also participate on the New Hampshire bus tour.

“I’m heading up Thursday night. We’ll have a bus of women senators traveling around the state doing campaign events, and I’m really excited about it,” said Gillibrand, who is seen as a possible future presidential candidate.

Democratic Sens. Amy Klobuchar Amy KlobucharEPA delivers win for ethanol industry angered by waivers to refiners It's time for newspapers to stop endorsing presidential candidates Biden marks anniversary of the Violence Against Women Act, knocks Trump and McConnell MORE (Minn.), Tammy Baldwin Tammy Suzanne BaldwinKeep teachers in the classroom Cher raised million for Biden campaign at LGBTQ-themed fundraiser Democrats seek balance in backing protests, condemning violence MORE (Wis.), Claire McCaskill Claire Conner McCaskillDemocratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally Missouri county issues travel advisory for Lake of the Ozarks after Memorial Day parties MORE (Mo.), Mazie Hirono Mazie Keiko HironoDemocrats unveil plan declaring racism a public health issue Overnight Defense: US, Russia trade blame over Syria incident | Pentagon calls out China's 'counterproductive' military exercises, missile test | Democrats press Esper on COVID-19 response Democrats press Esper on 'concerning' rise in Pentagon's COVID-19 cases MORE (Hawaii), Gillibrand and Stabenow campaigned for Clinton in Iowa. Gillibrand and McCaskill have also campaigned for her in Nevada.

Sen. Barbara Boxer Barbara Levy BoxerThe Hill's Morning Report - Presented by Facebook - Biden, Harris launch Trump offensive in first joint appearance Bottom line Polls show big bounce to Biden ahead of Super Tuesday MORE (D-Calif.) is planning to attend fundraisers for Clinton in her home state.

Some female senators say they haven’t pressed Warren.

“I think Elizabeth will make her decision when she wants to make her decision. I don’t think it affects Hillary’s candidacy at all,” Gillibrand said.

Rep. Dina Titus (D-Nev.), a longtime Clinton supporter, said while she hadn’t heard of the backroom conversations, “I think they are trying to get endorsements from as many people as they can get. She’s kind of a media darling, a real populist ... and having her endorsement would be a good thing.”

“I think it meant a lot to have her endorsement on the plan to reform Wall Street,” she said, adding that it was a good first step.

Clinton and Warren are two of the brightest lights of the Democratic Party, both with loyal followings. But their relationship has run warm and cold over the years.

Liberal activists tried to draft Warren to run for president against Clinton this year, despite many protestations that she was not interested.

In early 2013, Warren along with the rest of the Democratic women in the Senate signed a letter urging Clinton to run for president, but she has since clarified that it did not signify an endorsement.

Warren and Clinton have disagreed most pointedly on issues affecting Wall Street, which Clinton used to represent when she served as New York’s junior senator from 2001 to 2008.

Warren told journalist Bill Moyers in a 2004 interview that Clinton flip-flopped on key bankruptcy legislation after winning election to the Senate.

As first lady in the late 1990s, Clinton helped persuade President Clinton to veto the bill, which Warren argued at the time would hurt single mothers. But once Clinton was representing New York’s financial services industry in Congress, she voted for it.

“As Sen. Clinton, the pressures are very different. It’s a well-financed industry,” Warren told Moyers. “She has taken money from the groups, and more to the point, she worries about them as a constituency.”

Their relationship was sufficiently tense that Bill Clinton William (Bill) Jefferson ClintonD-Day for Trump: September 29 Trump job approval locked at 42 percent: Gallup If Trump doesn't know why he should be president again, how can voters? MORE did not campaign for Warren when she ran for the Senate against then-Sen. Scott Brown (R-Mass.) in 2012. The former president offered his support with an email fundraising solicitation, but he declined to appear with her in person.