WASHINGTON (AP) — Whether it was by coincidence or not, Hillary Rodham Clinton picked a fortuitous time to announce that she opposes the Keystone XL pipeline.

The longstanding criticism of Clinton's reluctance to say where she stands on allowing the pipeline project to go forward was buried in the headlines by arrival of Pope Francis for his first visit to the United States.

The next day, the pope's call to action on climate change fit with Clinton's reasons for opposing the pipeline. And it sets her up well for a few days of fundraising later this week in the San Francisco Bay area, where she was likely to face questions about her dithering among donors who are generally supportive of environmental causes.

The Democratic presidential candidate said Tuesday that she had concluded the ongoing debate over whether the pipeline should be built had hindered a larger effort to curb global warming.

"I think it is imperative that we look at the Keystone pipeline as what I believe it is — a distraction from the important work we have to do to combat climate change," Clinton said in Des Moines, Iowa. "And unfortunately, from my perspective, one that interferes with our ability to move forward to deal with all the other issues. Therefore I oppose it."

Environmentalists have warned that the extraction and transport of oil risks setting back the fight against man-made climate change. Big business argues that the Canada-to-Gulf of Mexico project would create valuable jobs.

On the presidential campaign trail, the debate over the pipeline has turned into a high-stakes fight for support and campaign cash as Clinton battles real and potential challenges. Opposing the pipeline puts her in line with rival Sen. Bernie Sanders, a favorite of the Democratic party's left wing. Clinton's opposition also sets out a marker as Vice President Joe Biden considers challenging her for the Democratic presidential nomination.

Signs quickly surfaced that Clinton's announcement was paying off for her.

Tom Steyer, a California-based environmentalist and top Democratic donor, quickly credited Clinton for joining with "thousands of Americans calling on President Barack Obama to reject the Keystone XL pipeline in favor of building an American economy powered by clean energy."

On Wednesday morning, the pontiff joined Obama at the White House and made an urgent call to address climate change, warning it "can no longer be left to a future generation."

To be certain, Clinton's unwillingness to offer a position had irritated liberals and environmentalists, and many winced when she said at a July town meeting in New Hampshire that if it was still undecided "when I become president, I will answer your question."

Clinton had said in 2010 that she was "inclined" to support the pipeline but had avoided taking a position after leaving the State Department in 2013.

In recent weeks, Clinton expressed impatience over the Obama administration's drawn-out deliberations and said last week in New Hampshire she was putting the White House "on notice" that she would soon announce her decision. Her campaign said the White House was briefed on Clinton's position prior to her comments and she privately made her opposition known in discussions with labor officials in recent weeks.

The announcement could set the boundaries for the environmental debate in next year's presidential election. Republican candidates like former Florida Gov. Jeb Bush said on Twitter that Clinton's decision proves she "favors environmental extremists over U.S. jobs."

Reince Priebus, the chairman of the Republican National Committee, meanwhile, said Clinton was being "blatantly dishonest" when she said her role at the State Department had prevented her from taking a position and said it was driven by concern about Biden joining the Democratic primary field.

Clinton said in a posting on Medium on Wednesday that she would seek to modernize the U.S.'s energy infrastructure and develop new partnerships with Canada and Mexico to fight climate change in North America. She reiterated interest in creating an infrastructure bank to unleash investments in clean energy and said she would strengthen pipeline safety regulations and work to replace the country's oldest pipes and riskiest train cars.

"American energy policy is about more than a single pipeline to transport Canada's dirtiest fuel across our country. It's about building our future," Clinton wrote.