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The House January 6 committee issued another round of subpoenas Tuesday as congressional investigators dig more deeply into illegitimate electors from key swing states that former President Donald Trump lost, who were put forward to try to justify delaying the certification of Joe Biden’s victory.

The committee issued subpoenas to six individuals, including two members of the Trump campaign and four prominent GOP officials from battleground states, as part of its investigation into the US Capitol attack on January 6, 2021.

“The Select Committee is seeking information about efforts to send false slates of electors to Washington and change the outcome of the 2020 election. We’re seeking records and testimony from former campaign officials and other individuals in various states who we believe have relevant information about the planning and implementation of those plans,” the panel’s chairman, Democratic Rep. Bennie Thompson of Mississippi, said in a statement.

The Trump campaign officials subpoenaed by the committee are Michael Roman, who was in charge of Election Day operations in 2020, and his deputy, Gary Michael Brown. Both “reportedly participated in efforts to promote allegations of fraud in the November 2020 election and encourage state legislators to appoint false ‘alternate’ slates of electors,” according to the committee.

The subpoena list also includes Republican state lawmakers from Pennsylvania and Arizona – Douglas Mastriano and Mark Finchem, respectively – as well as Kelli Ward, chairwoman of the Arizona Republican Party, and Laura Cox, former chairwoman of the Michigan GOP.

Last month the committee issued subpoenas for 14 Republicans from seven states who served on bogus slates of Trump electors in 2020 as part of the Trump campaign’s scheme to subvert the Electoral College.

In its subpoena letters to Roman and Brown, the committee writes that it has “credible evidence” that both former Trump campaign officials encouraged state legislators to appoint slates of fake electors to alter the results of the 2020 election.

The panel says it specifically is in possession of communications showing that Roman and Brown were involved in a coordinated strategy along with others from the Trump campaign to contact Republican members of state legislatures who represented states that Trump had lost to try to get them to “reclaim” their authority and support Trump by sending alternate slates of electors. The panel says that documents on file with the committee show that both Roman and Brown helped Trump campaign staffers in carrying out this effort. The committee also writes that Roman and Brown were aware of and participated in efforts to promote unsubstantiated claims about the 2020 election.

As for Mastriano, the committee is seeking to know more about his meeting with Trump in November 2020 and his involvement in planning for an alternate slate of electors to be presented. The panel also resurfaced tweets from Mastriano when he was at the Capitol on January 6 and said he had witnessed “agitators … getting in the face of the police” and “agitators … start pushing the police up the [Capitol] steps.”

Mastriano is currently running for governor in Pennsylvania.

The panel says it has evidence to show that Finchem communicated with leaders from the Stop the Steal organization about an event on the US Capitol grounds on January 6 where he was slated to speak. After the Arizona election results were certified for Biden, Finchem made repeated, unsubstantiated claims about the election being stolen and helped coordinate a hearing in Phoenix where members of Trump’s legal team repeated those claims. Finchem is currently running for Arizona secretary of state and has been endorsed by Trump.

Mastriano and Finchem signed a letter to former Vice President Mike Pence on January 5, 2021, asking him to delay certification of the electoral results on January 6.

A Democrat-led Senate Judiciary Committee report released last year revealed Mastriano’s correspondence with the Justice Department spreading debunked claims of fraud. Mastriano is one of the under-the-radar figures that the report singles out for further investigation for his efforts helping Trump try to subvert the election.

The House committee had already subpoenaed the phone of Ward and her husband, who filed a federal lawsuit to try to block that request. In its subpoena letter, the panel says it has documents that show Ward spoke to Trump and members of his staff about the election certification process in Arizona. Ward reportedly sent text messages to an Arizona election official asking the individual to “stop the counting.”

Her records and testimony would be of interest to the committee because she helped coordinate the fake electors in Arizona. The panel says Ward acted as a purported Electoral College elector in the effort to transmit a slate of alternate electors. Ward also was part of a public campaign to get Pence to throw the election to Trump while presiding over Congress’ certification of the Electoral College results on January 6.

As the former chairwoman of the Michigan Republican Party, Cox tried to delay the certification of election results in the state, and specifically raised concerns about Wayne County, which includes Detroit and become an area where Republicans concentrated their efforts to overturn the election and make baseless claims about fraud. In its subpoena letter to Cox, the committee asks to learn more about what she witnessed when Rudy Giuliani pressured Michigan state lawmakers to not certify the 2020 election results in their state and that doing so would be a “criminal act.” Giuliani, a central figure in Trump’s failed bid to overturn the election, has been subpoenaed by the committee as well and is reportedly engaging.

Cox joined Republican National Committee Chairwoman Ronna McDaniel in sending a letter to Michigan’s Board of State Canvassers in November 2020, asking to delay certification of the election results for 14 days to wait for an audit of Wayne County’s election results.

Cox and McDaniel sent the letter the day after Michigan Senate Majority Leader Mike Shirkey and former Michigan House Speaker Lee Chatfield flew to Washington, DC, to meet with Trump at the White House where Trump failed to pressure them to help overturn the election.

The last-ditch request from Cox and McDaniel to delay certification in Michigan was not possible because they were requesting an audit to be conducted before certification was complete, which goes against Michigan election law.

This story has been updated with additional developments Tuesday.

CNN’s Marshall Cohen contributed to this report.