Vice President Biden's sunglasses reflect the students in the audience at Yale University on May 17. (Jessica Hill/AP)

Joseph R. Biden Jr. has spent decades in national office, first as a senator and now as vice president, and he has an extensive record on the major issues in the campaign.

As a champion for progressive causes, he has several major accomplishments to his name. He's also taken several stances over the years that could make him vulnerable to criticism — if he runs for the Democratic presidential nomination next year.

Here is a quick review of where he stands on the big questions.

Crime

Biden's most consequential legislative achievement in his long career might be the crime bill he shepherded to passage as chairman of the Senate Judiciary Committee in 1994. That bill expanded the federal death sentence and created the "three-strikes" rule, requiring a life sentence without parole for anyone convicted of three violent or drug-trafficking felonies. The bill also increased the penalties for undocumented immigrants who enter the country illegally a second time after being deported.

States that likewise instituted harsher prison terms for convicts tried in their courts were more likely to receive grants from the federal government under the legislation, which also made billions of dollars available for the construction of new prisons and provided enough federal funding to add some 100,000 officers to police forces nationwide.

These days, some politicians on both sides of the aisle see the country's reliance on incarceration as misguided. While the causes of the steady and sustained decline in crime rates over the past two decades are still debated, most criminologists do not think that incarceration helped much if at all.

"It is time to end the era of mass incarceration," Democratic presidential candidate Hillary Rodham Clinton said earlier this year. Her husband — who signed Biden's crime bill into law as president — has said that the legislation "made the problem worse."

Experts say that the federal crime bill had only a small effect on the overall rate of incarceration nationally. Federal prisoners account for only about 1 in 10 inmates behind bars on any given day. The rest are in state facilities or local jails, and state officials had already begun to impose harsher sentences before Biden's bill became law. In other words, the legislation merely followed a change in attitude among policymakers and prosecutors rather than establishing a new paradigm across the country.

All the same, the bill clearly articulated a tough-on-crime attitude that Biden may have to explain if he enters the race.

Guns

While the punishments imposed by the crime bill could be a liability for Biden, he could also point to several provisions in the law that liberal Democrats will celebrate. For one, the bill banned assault weapons, a prohibition that remained in effect until it expired 10 years later. Biden said recently he thinks the ban should be reinstated.

[Everything you need to know about the assault weapons ban]

He has been an impassioned defender of stricter gun control throughout his career. Following the massacre at Sandy Hook Elementary School in Newtown, Conn., in 2012, President Obama gave him the job of moving a bill through Congress that would require background checks for private purchases, including guns bought and sold over the Internet and at gun shows. (Current law requires that only federally licensed dealers perform background checks on their customers.) That legislation failed because of a filibuster in the Senate.

There is some evidence that expanded background checks could reduce gun violence, although to be truly effective, a gun-control program would probably have to require gun owners to sell their weapons to the government, as Wonkblog has reported previously.

[What liberals don't want to admit about gun control]

Violence against women

The crime bill also included the Violence Against Women Act, a series of provisions designed to protect women from domestic abuse. The bill made federal money available to ensure that law enforcement had the manpower to pursue domestic-violence cases. Other funds went to shelters, where victims of abuse could stay if they weren't safe at home.

Advocates for women are divided on the effects of the law. For example, one provision, encouraged state authorities to require police officers to make arrests whenever domestic abuse is reported. The aim, in part, was to prevent police from discounting women's accusations against their abusers and leaving the scene of a serious crime without taking action.

Yet some research suggests that mandating arrests actually increases the rate of domestic homicide. Some victims of abuse might want the police to help calm an aggravated partner, but those victims might not want their partners to go to jail. If so, they might hesitate to call the police, even when a dispute is getting violently out of hand. In this respect, the law might have harmed some of the women it was intended to protect.

Although the act might have had unintended consequences, Biden has called the Violence Against Women Act his "proudest legislative accomplishment." More recently, he has been a leading figure in the Obama administration's efforts to reduce sexual violence on college campuses.

"No man has a right ever to raise his hand to a woman. Period. End of story," Biden said earlier this year.

Abortion

Biden has also been a supporter of abortion rights. Although the vice president is a practicing Catholic who believes that life begins at conception, he has said that women should be free to make their own choices about terminating pregnancies.

"Life begins at conception in the church's judgment. I accept it in my personal life," the former senator from Delaware said in a debate in 2012. "I refuse to impose it on equally devout Christians and Muslims and Jews.

"I do not believe that we have a right to tell … women they can't control their body," he added. "It's a decision between them and their doctor."

Climate change

By burning fossil fuels, humans are causing the planet to warm. Biden sees the change in the climate that has resulted as a "deadly serious" problem, he said Monday. He called it "the most consequential issue of our time."

He has also excoriated conservative politicians who deny the reality of global warming.

"I think it’s close to mindless. I think it’s like, you know, almost like denying gravity now," Biden said earlier this year.

Economic policy

Biden believes that the working class is no longer benefiting from an increasingly productive economy alongside the wealthy.

"It used to be when productivity went up in America, everybody got to share. The people who caused the productivity increase, they got to share. They got a piece of the action," the vice president said last month. "Something is wrong."

Biden was citing research by the liberal Economic Policy Institute, which suggests that in recent years, workers' wages have stopped increasing even though investments in technology and equipment are still allowing them to produce more per hour on the job. Clinton has used the same figures in her campaign.

Biden has served as the White House's liaison to Congress at crucial moments — in 2011 and again at the end of 2012, when he helped avert crises by negotiating deals on the budget. Liberal critics of the administration have complained that Biden and the administration gave up too much to Republicans, who didn't want to raise taxes on the wealthy or to borrow money to stimulate the economy.

It is difficult to know from his behavior in these negotiations how Biden really feels about the national debt, but he has a record of opposition to borrowing. As a senator 20 years ago, Biden supported a GOP-sponsored constitutional amendment that would have required the federal government to balance its budget every year.

Some economists have warned that such an amendment could have grave consequences. For one thing, it could destabilize the national economy, since the government would have to respond to an unexpected shortfall in revenue by spending less or taxing more to keep the budget balanced. Analysts in business and industry would have to try to predict these shifts in the government's finances to anticipate how the economy and their own firms would have to respond.

[Why Rand Paul wants to balance the budget every year]

Trade

Another major question for Biden's campaign is what he thinks about international trade. The Obama administration has negotiated a trade deal with several Asian and Latin American countries. Biden supports the deal and will help negotiate with lawmakers for its passage.

Unions, though, oppose the agreement, called the Trans-Pacific Partnership. Labor leaders predict the deal will put employees of U.S. exporting firms out of work.

[Tobacco companies lose as last pieces of a massive trade deal fall into place]

The vice president has reportedly sought support from union leaders in advance of an announcement about whether he will seek the presidency. Biden is a popular figure with labor.

"He’s a friend. He’s a brother. He’s a great champion of working men and working women," AFL-CIO President Richard Trumka said last month.

It is an open question, though, whether Biden can win their votes while supporting his boss.

The issue of trade has given Biden headaches in the past. "The thing I'm most unsure about is how you rationalize competition in trade policy," Biden said in a debate during his last presidential campaign in 2007. "I think that’s the single most difficult challenge that I will have as president."

Foreign policy

As a senator, Biden voted for the war in Iraq in 2003.  Later, he made a controversial proposal for a political settlement in the chaotic aftermath of the invasion.

Biden's plan was to give the Kurdish, Sunni and Shiite regions of the country more independence from the central government in Baghdad. Each would have its own government and more authority to manage its own affairs. Biden compared his plan to the agreement that ended the conflict in the Balkans, which he said separated that region along ethnic boundaries to prevent sectarian violence.

Critics of the plan worried that internally dividing the nation would lead to civil war. Maintaining a powerful central government in Baghdad didn't prevent internecine conflict, however. This year, the Islamic State has taken control in the western part of the country, with the support of some disaffected Sunnis.

And some experts on the region have suggested Biden's might have been the best approach all along. Had Sunnis felt that they had more say in their political affairs, they might have been less inclined to support a brutal insurgency.