WASHINGTON — Democratic members of the House Judiciary Committee have grown increasingly impatient with President Donald Trump’s attempts to block their Russia investigation. And now, some of them are urging the use of “stronger tools,” including impeachment proceedings, in order to strengthen their access to documents and witnesses, according to several lawmakers who spoke with NBC News.

Attorney General William Barr has resisted committee demands to release special counsel Robert Mueller’s full and unredacted Russia report to Congress and said he will not appear before the committee, which planned to use staff lawyers to question him.

In the past week, Trump has said he does not want Mueller to testify before the committee, although he said that decision is ultimately up to Barr, and sought to withhold classified portions of the report from Congress by invoking “executive privilege.”

“The obstruction stuff the president’s engaged in now is causing people to give this a second look,” Rep. David Cicilline, a committee Democrat from Rhode Island, said about impeachment.

“Whatever you think about the findings in the report itself, the blanket defiance of lawfully issued subpoenas and refusal to cooperate with constitutionally required oversight is — in and of itself — basis for impeachment,” Cicilline said in an interview.

He also noted that “contempt of Congress” was the third article of impeachment against President Richard Nixon. A formal impeachment inquiry would strengthen Congress’ hand in the court system, Rep. Jamie Raskin, D-Md., who sits on the committee, said.

“The more that the president denies us, the ordinary lawful demands for witnesses and documents, the more unified we are,” Raskin told reporters, calling Trump “the most impeachable president in the history of the United States.”

Other members of the Judiciary Committee, including chairman Jerrold Nadler, D-N.Y., remain firm that the committee needs to exhaust all other options before impeachment, which the public could view as a removal process rather than an effort to obtain testimony and documents.

“The short answer is, that may not be the best answer in this constitutional crisis,” Nadler said about impeachment.

The growing sentiment toward more aggressive measures explains comments made last week in a private caucus meeting by House Speaker Nancy Pelosi, who has been urging a cautious approach to impeachment talk. Pelosi argued that Trump is “self-impeaching” himself through his actions, adding, “he’s doing our work for us” — statements that seemed to indicate more openness to a conversation about impeachment.

Previously, Pelosi had insisted that Trump is “not worth” impeaching.

The Mueller report outlined a “sweeping and systemic” attack on the United States directed by the Russian military, numerous ties between Russians and Trump campaign officials, and multiple instances of potential obstruction of justice by Trump.

Democrats argue that Barr’s summary, made public weeks before a redacted version of the report was released, set a false narrative that Trump had been cleared of both collusion with Russia (the report only addressed criminal conspiracy) and obstruction of justice.

Support for the president among congressional Republicans — particularly in the Senate — has remained resilient, leaving impeachment an option with little chance of success. Instead, Democrats have pursued a strategy of holding extensive public hearings to highlight a report they are concerned many Americans have not read, and have sought access to more information used in the Mueller investigation itself.

The administration’s decisions to fight Congress on those requests are straining that approach by blocking documents and witnesses, Democrats say.

And it’s not only the Russia investigation. The Washington Post reported last weekend that Trump and his allies are blocking more than 20 separate investigations, in what experts are calling the “most expansive White House obstruction effort in decades.”

“While I understand Speaker Pelosi and the leadership’s desire to take it slow and let the investigations proceed, I believe President Trump should be impeached,” said Rep. Steve Cohen, D-Tenn., another committee member.

“The facts that are adduced in impeachment hearings will be sufficient for most of the American people and, if the Republican Senate doesn’t see the truth laid out before their eyes, they will have to face the ire of their constituents and the shame of history,” Cohen said.

The committee had hoped Mueller would testify this week, and Trump’s actions have already thrown a wrench in the plan, the members said.

Now Nadler is giving Mueller time to determine whether Trump’s claim of executive privilege will limit his testimony and even whether Mueller should wait until he is no longer a Department of Justice employee to testify, according to two sources familiar with the talks.

The Department of Justice declined comment on why Mueller has not yet agreed to testify.

In remarks to reporters last week, Nadler said Mueller might rather come as a private citizen rather than a Department of Justice employee. “He may prefer to do that because he’s then more free” and “that should be only a matter of weeks anyway,” Nadler told reporters. He also said he may have to subpoena Mueller if necessary.

Members are discussing other options for moving the process along as Democrats believe Trump’s strategy is to “run out the clock” on Congress’ ability to investigate him and his administration. Pelosi is considering bundling contempt votes on the House floor given the number of subpoenas that the White House is telling officials not to comply with.

Finally, some members believe beginning impeachment proceedings could be a smarter political option than waiting until just before the November election.

Other options under discussion include using a little used authority called inherent contempt, which allows Congress to issue fines or even jail noncompliant witnesses or impeaching Barr.

“Everyone acknowledges there’s a problem here but we’re not doing enough to solve the problem,” said one lawmaker, who spoke on condition of anonymity as frustration builds in the caucus for a tougher approach.

One leadership aide was more blunt: “Do it now, get it out of way, say you delivered for the base,” the aide said. “There will be so much evidence in front of people. You look weak because you didn’t have the fortitude to do it in the beginning.”