North Dakota Sen. Heidi Heitkamp will vote to confirm CIA Director Mike Pompeo as President Trump's secretary of state on the Senate floor, and will be a key Democratic vote to the former House lawmaker’s bid.

"Pompeo demonstrated during this nomination process and during our meeting in March that he is committed to empowering the diplomats at the State Department so they can do their jobs in advancing American interests," Heitkamp said in a Thursday afternoon statement.

“The role of the State Department is to support our diplomatic missions to avoid conflict, support American interests, and stand up for our allies,” she added. “[H]aving a leadership team in place is essential to carrying out those jobs.”

Her decision all but guarantees Pompeo’s confirmation, which faces historic opposition as Kentucky Republican Rand Paul and the Democratic members of the Foreign Relations Committee plan to vote against him when the panel convenes Monday. Republicans have a bare 51-49 majority in the Senate, so Paul’s opposition — combined with Senate Armed Services Committee Chairman John McCain’s absence due to health reasons — meant Pompeo was needed to turn a "no" vote into a "yes" vote to be confirmed.

Pompeo’s promise to empower State Department officials was a key part of his push for Senate support. Secretary of State Rex Tillerson faced heavy criticism for failing to nominate diplomats to numerous posts and developed a reorganization of the State Department bureaucracy that drew skepticism from lawmakers.

“[State Department staff] also shared how demoralizing it is to have so many vacancies and, frankly, not to feel relevant,” Pompeo said in remarks prepared for his confirmation hearing. “I’ll do my part to end the vacancies, but I’ll need your help. And I will work every day to provide dedicated leadership and convey my faith in their work — just as I have done with my workforce at the CIA.”

That wasn’t enough for Democratic critics on the Foreign Relations Committee who took aim at Pompeo’s past statements that only “regime change” would stop Iran from pursuing nuclear weapons, along with social policy disputes such as the former lawmaker’s opposition to gay marriage and taxpayer funding for Planned Parenthood.

“I was pleased to hear Director Pompeo pledge support for the mission and personnel of the Department,” New Jersey Sen. Bob Menendez, the top Democrat on the panel, said Wednesday. “But let’s be clear: this is a minimum declaration we should expect from any Secretary. More broadly, Director Pompeo did little to assuage my concerns about the Administration’s deafening lack of strategic vision for any of our major global challenges.”

Menendez also faulted Pompeo for failing to reveal that he traveled to North Korea over Easter weekend for preliminary meetings, in advance of President Trump’s highly-anticipated summit with dictator Kim Jong Un.

In the face of such opposition, Pompeo courted red-state Democrats who are not members of the committee, such as Heitkamp, to reinforce his bid. White House and congressional allies have stepped up that pressure as the target Democrats remained on the fence in the days leading up to the vote.

"I cannot imagine that senators like Joe Manchin from West Virginia and Joe Donnelly from Indiana and Heidi Heitkamp from North Dakota, who are facing reelection in states that our president won by landslide elections, are going to oppose an obviously qualified nominee for whom they voted last year," Sen. Tom Cotton, R-Ark., told reporters in a Wednesday call hosted by the White House. "If they do so, and they’re up for reelection, they may suffer the consequences."

Heitkamp cited North Korean diplomacy as a major factor in her thinking about Pompeo’s potential as the nation’s top diplomat.

“If he’s confirmed, I’ll hold Mr. Pompeo accountable to make sure he advances or country leadership in the world and supports our embassies — including by filling critical jobs that have bee vacant, like for the U.S. Ambassador to South Korea,” she said. “We need to seek a diplomatic solution in North Korea and we need to make sure that any discussions support the goals of the U.S.”