(CNN)Sen. Josh Hawley blocked quick consideration of President-elect Joe Biden's Homeland Security nominee, Alejandro Mayorkas, on Tuesday, leaving the third-largest federal department without confirmed leadership as it faces national security concerns, a pandemic and an incoming president prepared to roll out ambitious immigration plans.
Sen. Josh Hawley (R-MO) asks questions during a Senate hearing.
The Missouri Republican's decision stemmed from an exchange with Mayorkas hours earlier during the nominee's confirmation hearing before the Senate Homeland Security Committee.
"Mr. Mayorkas has not adequately explained how he will enforce federal law and secure the southern border given President-elect Biden's promise to roll back major enforcement and security measures," Hawley said in a statement.
"Just today, he declined to say he would enforce the laws Congress has already passed to secure the border wall system. Given this, I cannot consent to skip the standard vetting process and fast-track this nomination when so many questions remain unanswered," he continued.
Transportation Security Administration head David Pekoske is expected to temporarily take over as acting Homeland Security secretary when the Biden administration enters office Wednesday, according to Department of Homeland Security spokesperson Alexei Woltornist.
Under President Donald Trump, DHS has been rattled with consistent leadership turnover, including in the final weeks of his administration. Earlier this month, Chad Wolf stepped down from his post as acting secretary following intense scrutiny over the validity of his appointment.
Federal Emergency Management Agency Administrator Pete Gaynor assumed the role of acting DHS secretary, becoming the sixth secretary under the Trump administration. The department hasn't had a Senate-confirmed secretary since April 2019.
Gaynor told his workforce he would fill the job until "January 20 when President-elect Biden is inaugurated."
In a statement to CNN, Sean Savett, a Biden transition spokesperson, called Mayorkas "one of the most knowledgeable homeland security experts in the country."
"The Senate held swift confirmation votes for the DHS Secretary nominee in 2009 and 2017 in order for them to start on day one for good reason," Savett said. "Senator Hawley's threat to disrupt historical practice and try to leave this vital position vacant is dangerous, especially in this time of overlapping crises when there is not a moment to waste."
Hawley questioned Mayorkas on Tuesday about funds appropriated for the US-Mexico border wall and whether they would be spent as intended, in light of Biden's pledge to halt wall construction.
While Mayorkas committed to following through with Biden's promise, he maintained he'd do so "in adherence to the laws that guide us."
"Senator ... if I may strike at the fundamental point that I believe you are inquiring of, which is, will I follow the law and the execution of my responsibilities should I have the privilege of serving as the secretary of Homeland Security? And the answer is yes, I will follow the law," Mayorkas said, adding that he would need to understand "what the law provides with respect to the obligation of funds to construct the border wall and see what the opportunities are to discontinue any such obligations if in fact the law permits and act accordingly."
The government has long-standing authority to terminate contracts, though it comes at a cost, according to contracting experts. A US official previously told CNN that some contracts can be modified. But the department's mission extends beyond immigration. DHS is also playing a leading role in securing the US Capitol for the inauguration and is involved in responding to the coronavirus pandemic.
"Our nation is facing unprecedented crises and threats to American national security, from the devastating Coronavirus pandemic to massive cyber breaches across government and the private sector -- and as we have seen too clearly in recent weeks -- rising domestic terrorism and anti-government violence. The Department of Homeland Security is the lead agency charged with combatting these threats and more, and it needs qualified, Senate-confirmed leadership in place immediately," Democratic Sen. Gary Peters of Michigan, the ranking member of the Senate Homeland Security Committee, said in a statement, urging his colleagues to confirm Mayorkas.
Sen. Chris Murphy said Tuesday that Hawley's decision is putting the "country's security at risk."
"I mean, you know, all he can do is slow down the nomination and put the country's security risk especially in a moment when domestic terrorists are plotting another attack against this nation," the Connecticut Democrat said when CNN's Phil Mattingly asked for his reaction to Hawley's objection.
Murphy continued, "But Senator Hawley and his crowd are pretty clear that they put their political interests ahead of the security interests of the country and that obviously is not changing."
This story has been updated to note that Transportation Security Administration head David Pekoske is expected to step in as acting Homeland Security secretary temporarily.
