WASHINGTON (AP) — Special counsel Robert Mueller's first — and possibly last — public statement on the Russia investigation is fueling fresh calls on Capitol Hill to begin impeachment proceedings against President Donald Trump, a step that Democratic leaders have so far resisted.

Surprising Washington with brief remarks Wednesday, Mueller indicated it's up to Congress to decide what to do with his findings. The special counsel reiterated that, bound by Justice Department policy, charging a sitting president with a crime "was not an option." But he also stressed he could not exonerate Trump. Instead, he said, "the Constitution requires a process other than the criminal justice system."

With Mueller closing his office and no further comments expected, it all amounted, for some, to an open invitation for Congress to launch impeachment proceedings.

"He's asking us to do what he wasn't allowed to — hold the president accountable," said Rep. Val Demings, D-Fla., a member of the House Judiciary Committee, the panel with impeachment power.

"We have one remaining path to ensure justice is served," said Sen. Cory Booker of New Jersey, a Democratic candidate for president. "It's clear that the House must begin impeachment proceedings. No one is above the law."

But top Democrats, with almost no support from Republicans, are hesitant to go it alone on an impeachment inquiry that House Speaker Nancy Pelosi has warned would be divisive for the nation. Steered by Pelosi, they prefer to continue the work of investigating the president and building a case, as she often says, wherever it leads.

Staying the course, Rep. Jerrold Nadler, D-N.Y., the chairman of the Judiciary Committee, at a news conference in New York stopped short of calling for an impeachment inquiry.

"All options are on the table and nothing should be ruled out," Nadler said Wednesday.

Nadler's committee is among several conducting dozens of probes in the Democratic-controlled House into subjects such as Trump's tax returns, the handling of the Russia probe and the running of government. The chairman vowed to continue investigating, even as some on his panel say opening a formal impeachment proceeding would strengthen their hand in the legal battles over documents and testimony.

"Given that special counsel Mueller was unable to pursue criminal charges against the President, it falls to Congress to respond to the crimes, lies and other wrongdoing of President Trump - and we will do so," Nadler said in a written statement issued immediately after Mueller's remarks.

Before Mueller's unexpected appearance, Democratic leaders had tamped down increasingly vocal voices calling for an impeachment inquiry. Pelosi sent lawmakers home for a weeklong recess brushing back the pro-impeachment faction, urging her caucus to stick with the step-by-step approach of investigations. They hoped to hear directly from Mueller in a high-profile hearing that could help focus public attention.

But now that Mueller has made clear the work ahead won't likely include him — announcing the special counsel's office is closing and he's resigning his position — it's igniting new urgency on Capitol Hill to pick up where the special counsel left off.

Rep. Seth Moulton of Massachusetts, another Democratic presidential hopeful, said, "Mueller did his job. Now it's time to do ours. Impeachment hearings should begin tomorrow."

While some Democrats want to focus on investigating Trump, building the case in the public, as happened during the Watergate era under Richard Nixon, others, including some new voices Wednesday, say Mueller has all but punted the issue to Congress.

Even the speaker is showing signs of impatience.

During a Tuesday commencement address at San Francisco State University, Pelosi quoted Martin Luther King Jr. in warning against "gradualism." She said, "We must recognize the urgency of our times now and the need for boldness and courage to save and strengthen America."

Pelosi said Wednesday that Mueller made clear that he did not exonerate the president when he stated, "If we had confidence that the president clearly did not commit a crime, we would have said so."

"The Congress will continue to investigate and legislate to protect our elections and secure our democracy," Pelosi said. "The American people must have the truth."

Mueller's report did not establish a criminal conspiracy between Russia and the Trump campaign to sway the outcome of the 2016 presidential election in Trump's favor. Investigators examined nearly a dozen episodes involving the president for potential obstruction of justice but ultimately reached no conclusion on whether Trump had illegally tried to stymie the probe.

Mueller made clear his desire to avoid testimony, declaring the report his final word on the matter. He said it wouldn't be "appropriate" for him "to speak further about the investigation."

Nadler would not say whether he would compel Mueller to testify, as he has threatened to do. But he hinted that he may not pursue an aggressive approach against the special counsel, saying, "Mr. Mueller told us a lot of what we need to hear today."

Republicans, as they have done since Mueller's report was released, called for Congress to move on.

The GOP chairman of the Senate Judiciary Committee, Sen. Lindsey Graham of South Carolina, said that Mueller "has decided to move on and let the report speak for itself. Congress should follow his lead."

Graham has said his committee doesn't need Mueller to testify. Georgia Rep. Doug Collins, the top Republican on the House Judiciary panel, had supported Democratic requests for Mueller's House testimony but appeared to be satisfied by the special counsel's comments Wednesday.

"While I had hoped he would come before the committee and answer questions from lawmakers, Robert Mueller has led an extraordinary life of public service and is entitled to his life as a private citizen once again," Collins said.

But at least one Republican isn't ready to move on: Rep. Justin Amash of Michigan, who has become the sole GOP voice in Congress urging impeachment proceedings.

"The ball is in our court, Congress," Amash tweeted.

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Associated Press writer Elana Schor in Washington contributed to this report.