Sen. Bernie Sanders Bernie SandersButtigieg stands in as Pence for Harris's debate practice Bernie Sanders warns of 'nightmare scenario' if Trump refuses election results Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (I-Vt.) is taking a shot at Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE on her slow decision to oppose the Keystone XL pipeline.

“How many years do you have to think about whether or not we excavate and transport the dirtiest fuel in the world?” Sanders said in a meeting with the Boston Globe editorial board on Thursday, referring to the Democratic presidential front-runner.

ADVERTISEMENT

“It didn’t take me too long to think about that," he added.

President Obama announced on Friday that he would reject the proposal to build the pipeline to bring oil sands from Canada to the Gulf Coast.

Environmental and liberal groups waged a long fight against the project, which was under review for seven years.

Clinton, though, only announced her opposition to the pipeline in September. Clinton, who was secretary of State during part of the department's review of the project, has defended herself from critics by noting that she has long championed policies to address climate change.

Sanders has been throwing more jabs at Clinton in recent weeks as he seeks to close the gap in the race.

He further contrasted himself with Clinton on Friday, saying he disagrees with her “on virtually everything.”

He pointed to issues he and Clinton disagreed on when she was also serving in the Senate, including his opposition to the Iraq War and the Defense of Marriage Act.

“You ask me about the differences between Hillary Clinton and myself? I have taken tough votes throughout my entire life,” Sanders said.

He also said that he should have come out more strongly against Clinton’s charges of sexism.

“We let her get away with it,” Sanders said. “We didn’t handle it as well as we should have.”

Clinton alleged that Sanders made a sexist remark when he said that people should stop "shouting" about guns after she raised his stance on gun control during the first Democratic debate.

She later said that "sometimes when a woman speaks out, some people think it's shouting."