Johnson will replace former department chief Janet Napolitano, who left her post last month to become the next president of the University of California. [WATCH VIDEO]
The administration's "mismanagement" of America's borders, particularly the southern barrier between Texas, Arizona and Mexico has led to a stead uptick of violence and drug trafficking along that southern corridor.
"Rather than selecting someone who knows the unique dynamics of [border security], President Obama has tapped one of his former New York fundraisers," Cornyn said of Johnson's pending nomination.
"We need someone who knows how to secure the border, not dial for dollars," he he added.
Cornyn's criticisms of Obama's leadership decisions at the DHS fell in line with fellow Republican Sen. Jeff SessionsJeff SessionsSanders: 'What do the Russians have on Mr. Trump?' Poll: Trump controversies make him more popular among supporters More than ever, Justice must demand a special prosecutor for Trump-Russia probe MORE (Ala.), who called the agency the "most mismanaged" department in the federal government.
“Department policies have collapsed enforcement and destroyed the morale of our officers," Sessions said Thursday.
The Alabama Republican argued those same problems will only worsen under Johnson's leadership.
"This huge department must have a proven manager with strong relevant law enforcement experience, recognized independence and integrity, who can restore this department to its full capability," Sessions said.
For its part, the White House vehemently defended the Johnson pick for the DHS.
A senior administration official said that Johnson was selected for his "sound judgment and counsel" as the Pentagon's top lawyer, where he signed off on every military operation approved by the president and secretary of Defense and led a legal staff of 10,000.
"Johnson is consistently praised by current and former members of the military as an honest broker with a firm understanding of the law," the official said.
Johnson was at the center of developing some of the administration's most sensitive national security policies, the official said.
Johnson left the Pentagon at the end of 2012 to return to private practice after serving as the Defense Department’s top lawyer through Obama’s first term.
He played a role in helping craft the Obama administration’s counterterrorism policies, and he was a crucial player in the administration’s effort to repeal the ban on gay service members serving openly in the military.
The nomination was first reported by The Daily Beast.