Sen. Richard Blumenthal, D-Conn., told reporters Thursday he "can name between five and 10 Republicans who are seriously considering voting against" Matt Gaetz's nomination for attorney general.

Blumenthal said the senators are also "insisting that there be a vote," after Trump has urged the incoming GOP Senate majority to embrace recess appointments to install members of his Cabinet.

"Republicans, as well as Democrats, are absolutely aghast at the idea that we would allow a recess appointment of the top judicial officer in the United States of America; that is absolutely abhorrent to the powers and traditions of the United States Senate and the Constitution," Blumenthal said.

Blumenthal, who is a member of the Senate Judiciary Committee, has also demanded that the House ethics report on Gaetz regarding allegations of sexual misconduct and illicit drug use be released following Gaetz's resignation from Congress.

-ABC News' Rachel Scott, Benjamin Siegel and Hannah Demissie

On the House floor Thursday afternoon, the clerk read a resignation letter from Florida Rep. Matt Gaetz regarding his immediate departure from Congress, following Trump's nomination of him for attorney general.

"I hereby resign as a United States representative for Florida's 1st congressional district, effective immediately. And I do not intend to take the oath of office for the same office in the 119th Congress to pursue the position of attorney general in the Trump administration," the House clerk read from the letter, which was submitted on Wednesday.

In light of Gaetz's resignation, the new House breakdown is 220 Republicans, 213 Democrats and two vacancies.

-ABC News' Lauren Peller

When asked if he believes Matt Gaetz could be confirmed as attorney general, the incoming Senate majority leader told ABC News he doesn't know until they start the Senate confirmation process.

"I don't know until we start the process, and that's what we intend to do with him and all the other potential nominees," Sen. John Thune said. "None of this stuff's formal yet, but you know, when it is, we expect our committees to do their jobs and provide the advice and consent that is required under the Constitution."

Gaetz, who had been under a House ethics investigation over allegations of sexual misconduct and illicit drug use, resigned from Congress on Wednesday following his nomination for attorney general by Trump. Sources told ABC News the committee was preparing to meet this week to deliberate over whether to release a final report on the matter.

Sen. Dick Durbin, D-Ill., who currently chairs the Senate Judiciary Committee, has called for the report's release, saying Gaetz's resignation raises "serious questions" about its contents.

"We cannot allow this valuable information from a bipartisan investigation to be hidden from the American people," Durbin said in a statement Thursday.

House Ethics Committee Chairman Rep. Michael Guest, R-Miss., refused to discuss the confidentiality of the investigation into Gaetz.

"What happens in ethics is confidential," Guest told reporters Thursday.

-ABC News' Hannah Demissie, Isabella Murray, Lauren Peller, Arthur Jones II and Mariam Khan

Homeland Security Secretary Alejandro Mayorkas said he is committed to a "smooth transition" at the department he leads.

"I am committed to a smooth transition to ensure that the incoming Secretary and their team understands the challenges that we face on the homeland, and to ensure that the team understands, appreciates and is in a position to advance the capabilities that we have developed and strengthened to address those challenges successfully," Mayorkas said on a conference call with reporters on a separate topic on Thursday. "The transition team has not landed here at the Department of Homeland Security."

He said the department is still implementing President Joe Biden's policies.

"We are no different than any administration that perceives us in so far as we have a president now and we are executing the policies of this president. The president-elect will determine what policies to promulgate and implement, and that is, of course, the president-elect's prerogative."

South Dakota Gov. Kristi Noem was nominated by Trump for the DHS secretary position, which requires Senate confirmation.

-ABC News' Luke Barr