Former deputy attorney general Tom Dupree said Thursday that it was "intriguing" to hear that a Senate committee controlled by Republicans is demanding that Donald Trump Jr. return to testify.

The Senate Intelligence Committee, chaired by Sen. Richard Burr, R-N.C., issued a subpoena to the 41-year-old real estate executive this week.

A statement from Trump Jr.'s camp slammed Burr as a "so-called Republican" and called him "too cowardly to stand up to" Vice Chairman Mark Warner, D-Va., whom the statement referred to as Burr's apparent "boss."

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"That's a bit intriguing," Dupree said of the subpoena on "America's Newsroom," adding that until this point, the call for additional witnesses and a "follow-up to [Robert] Mueller ... has been divided along partisan lines."

Dupree said the subpoena showed that there remain some Republicans who think it may not be "case closed" in regard to the Trump-Russia investigation.

House Minority Leader Kevin McCarthy, R-Calif., ripped those fellow Republicans calling for Trump Jr. to return to Capitol Hill, saying in a tweet that "endless investigations by either party won't change the fact there was NO collusion."

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"It's time to move on," McCarthy wrote.

Responding to the news, Trump Jr. retweeted Burr's North Carolina counterpart, Sen. Thom Tillis, who tweeted "case closed," and called for Congress to "move on" and work toward "real issues facing America."