"Congressional subpoenas for testimony are not optional", House Speaker Paul D. Ryan (R-Wis.) said Wednesday, promising that "we will do what we need to do to protect this branch of government".
Page was schedule to testify before Congress Wednesday.
Mr. Nadler called the Republicans' investigation into bias by the Justice Department and FBI surrounding probes related to the 2016 election a "political charade" to "elevate far-right conspiracy theories".
The text messages exchanged between Strzok and Page while they worked on the Hillary Clinton email investigation and the probe into President Donald Trump and Russian Federation have been cited by Trump and his allies as key evidence that the FBI's investigation is biased against the President. Trump said of the decision.
The president has repeatedly painted Mueller's investigation as a tainted witch-hunt led by Democrats. "Congressional subpoenas for testimony are not optional". Ryan and others have threatened contempt several times over the past year as other witnesses have defied subpoenas in the House intelligence committee's now-closed Russian Federation investigation and as the Justice Department has withheld documents, but they have yet to hold a vote on it.
Even several committee Republicans don't expect that Page will seriously consider taking up the offer for her to appear at the hearing Thursday, to be questioned alongside Strzok.
I am on Air Force One flying to North Atlantic Treaty Organisation and hear reports that the Federal Bureau of Investigation lovers, Peter Strzok and Lisa Page are getting cold feet on testifying about the Rigged Witch Hunt headed by 13 Angry Democrats and people that worked for Obama for 8 years. But her lawyer, Amy Jeffress, pushed back, arguing in a statement that Page needed "clarification of the scope of the Committee's interest in interviewing her and access to relevant documents" before she sat for an interview with the panels.More news: Dem senator: Kavanaugh would 'turn back the clock' on women's healthcare
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The two committees' "bullying tactics here are unnecessary", she added. "We expect them to agree to another date so that Lisa can appear before the committees in the near future".
"Through her actions and words, Lisa has made it abundantly clear that she will cooperate with this investigation", Jeffress said.
The Judiciary and Oversight panels have already spent much of the summer holding hearings and interviews critical of the Federal Bureau of Investigation and Justice Department. When he returns to Capitol Hill for Thursday's hearing he will be speaking publicly about the messages for the first time.
In an interview with the Wall Street Journal earlier this year, Trump said the text between Strzok and Page amounted to "treason" and had exposed an Federal Bureau of Investigation plot against him.
Mueller, a Republican, removed Strzok from the inquiry when he learned about the text exchanges and Page has left the Federal Bureau of Investigation.
The Justice Department investigated text exchanges between the two in a June report conducted by the Inspector General.