Washington (CNN) President Donald Trump's announcement on Sunday of Mark Morgan as the nominee to lead Immigration and Customs Enforcement caught the agency and lawmakers by surprise, and his Senate confirmation is by no means assured.

"I am pleased to inform all of those that believe in a strong, fair and sound Immigration Policy that Mark Morgan will be joining the Trump Administration as the head of our hard working men and women of ICE. Mark is a true believer and American Patriot. He will do a great job!" Trump tweeted.

This is Trump's second nominee to lead ICE after abruptly pulling the nomination of Ron Vitiello last month and comes amid a shakeup at the Department of Homeland Security, which now has several acting leaders in key positions. ICE is the enforcement arm of the department and a critical component of the President's immigration agenda.

Matt Albence will continue to serve as acting ICE director, Trump said.

The White House has yet to formally announce Morgan's nomination and send it to the Senate Homeland Security Committee, according to two committee aides.

The agency was caught up in the department shake-up last month when Vitiello's nomination was suddenly pulled at the urging of White House adviser Stephen Mille r. Vitello was on the cusp of Senate confirmation.

Just as the agency was blindsided by the withdrawal of Vitiello's name, ICE leadership had no advance notice of the White House announcement Sunday, according to a senior DHS official.

When asked about his reaction to the President's decision to nominate Morgan, Vitiello told CNN: "I wish him all the best."

"The ICE workforce is very dedicated and as they helped me get up to speed on the issues, they will do the same for him," Vitiello added.

The last confirmed ICE director was Sarah Saldaña, under President Barack Obama. Since then, Daniel Ragsdale, Tom Homan, Ron Vitiello and Albence have served in an acting capacity.

There is concern at the agency with the "on-again, off-again, interchangeable parts of leadership," the official said, referring to the lack of consistent leadership at the top of the agency.

"Is anyone confirmable for ICE, especially after putting so much shoe leather and sweat equity into the last confirmation?" said another DHS official.

A few days prior to the President's announcement, Morgan told Fox's Lou Dobbs in an interview that "no one from the White House has called me or asked me or had a conversation at all at any level," though he added that he'd "say yes in a heartbeat."

Morgan briefly served as Border Patrol chief under the Obama administration before leaving the post in January 2017. He previously spent two decades at the FBI.

Two Senate Republican aides and a Democratic aide said senators would review Morgan's qualifications and record, as is custom with all nominees.

Tenure at Border Patrol

Although Vitiello was expected to eventually be confirmed, he faced strong opposition from ICE union leadership, questions from lawmakers about his record and past comments, as well as Senate committee vote delays.

Like Vitiello, Morgan will also likely face questions over his record, particularly his vocal support for a border wall and Trump's national emergency declaration. In congressional testimony last month, he backed the administration's stance on asylum and advocated for a "border-wide" expansion of the Trump policy that requires some asylum seekers to stay in Mexico for the duration of their immigration hearings.

Morgan said that in order to achieve "lasting, effective" border security, Congress must grant the authority to detain asylum seekers while they are going through their immigration proceedings, as well as changing the laws to ensure children, who are not victims of trafficking or persecution, are returned to their home, regardless of their country of origin.

Morgan's tenure as Border Patrol chief did not sit well with the Border Patrol union, the first law enforcement union to endorse Trump. In a 2016 op-ed , the union called Morgan a "disgrace to the Border Patrol."

The union wanted him fired, said former CBP Commissioner Gil Kerlikowske, who served in the Obama administration. Shortly after assuming the role of chief, Morgan left his position as head of Border Patrol only a few months after taking the job. The decision to oust Morgan came directly from the White House, according to Kerlikowske.

Vitiello took his place as chief of the Border Patrol when he was appointed by current acting Homeland Security Secretary Kevin McAleenan in January 2017.

Vitiello, who worked with Morgan at CBP, said that Morgan's time leading Border Patrol "was quite a challenge for the culture, but we worked through it."

He said that the CBP "leadership team worked their asses off for his success," referring to Morgan's tenure as chief of the agency.

Then-FBI Director James Comey "loaned" Morgan to CBP when Kerlikowske asked for a top-level executive to "kick start internal affairs." (Internal affairs had previously been outsourced).

"He did an excellent job" for the six months he was helping CBP to form the agency's own internal affairs unit -- the Office of Professional Responsibility, said Kerlikowske, who later appointed Morgan as chief of the Border Patrol.

National Border Patrol Council President Brandon Judd told CNN Tuesday that he believes "[Morgan's] time with ICE is going to be a lot different than it was with the Border Patrol."

Judd pointed out that ICE's largest division is investigations, which is "Morgan's bread and butter," having come from the FBI. "The Border Patrol, on the other hand, has no investigative branch, which is one of the reasons why he wasn't the best fit," Judd said.

In a statement Monday, McAleenan also praised Morgan's experience as a career civil servant. "The depth of his experience will be an asset to the Department and I look forward to working with him," he said.