Hillary Clinton has made a lot of promises on the campaign trail: A $12-per-hour minimum wage. Debt-free college. A crackdown on big banks. But is all of this just positioning to appeal to an electorate trying to decide between her and Bernie Sanders? Or would she actually try to do any of this if she were elected?

The research suggests she would — despite the common criticism that politicians will say anything to get elected and then change their minds, most presidents try to keep the promises they made on the trail.

To many people, that's counterintuitive. Campaign promises that are broken become the stuff of lore, such as George H.W. Bush raising taxes after the famous line, "Read my lips — no new taxes" at the Republican National Convention in 1988.

But those broken promises stand out because they're exceptions, not the rule. Research by political scientists has found that campaign promises really do matter, and that once elected, politicians mostly try to do exactly what they said they would. And when they don't, it's usually due to a lack of cooperation from Congress, not a craven flip-flop.

Politicians keep their promises — and they have for years

When President Obama was elected, PolitiFact began tracking how his campaign promises would fare when he was in office. The website has kept it up for nearly seven years, with more than 500 promises from the 2008 and 2012 campaigns on the "Obameter."

So far, Obama has kept 45 percent of his promises and compromised on another 25 percent — and a compromise, in this case, includes things like his promised "universal" health care law having holes in it due to states that opted out of Medicaid. The evaluation doesn't distinguish between big and small promises, so universal health care and repealing the Defense of Marriage Act are on the same footing as cap and trade and bipartisanship.

Still, it estimates Obama has only broken 22 percent of his promises, and has kept or compromised on the majority. And some of these "broken" promises, along with others classified as stalled, ran into implacable congressional or judicial opposition. In other words, it wasn't for lack of trying.

That makes Obama about average. In 1984, political scientist Michael Krukones studied presidents from Woodrow Wilson to Jimmy Carter and found that American presidents kept about 75 percent of their campaign promises. Follow-up research from Colleen Shogan studied Ronald Reagan and Bill Clinton and found that in their first terms, the two presidents were very successful at getting their major campaign promises enacted, although they struggled in later years.

And it's not just presidents: Members of Congress who mention issues during their campaigns are more likely to introduce bills related to those issues once they're elected, Tracy Sulkin found when she studied congressional campaigns from 1998 through 2002. It didn't matter whether candidates spoke in vague generalities or proposed specific plans — either way, they were more likely to follow through on the issue once in office.

This holds true in the US and around the world. Politicians can't deliver everything they promise, but they usually try. And they succeed more than half the time. An overview of 21 studies of campaign promises from the United States, Canada, the Netherlands, the United Kingdom, and Greece found that on average, political parties fulfilled 67 percent of their promises.

"Campaign rhetoric does matter," Shogan wrote. "It provides a blueprint of the policy agenda presidents pursue if elected. In spite of the frivolity, mindless photo-ops, and ridiculous pancake breakfast appearances, campaigns are a substantive democratic exercise."

Vague rhetoric isn't nearly as predictive as specific promises

Of course, no president has kept all his promises. And the fact that in general presidents are pretty consistent might be cold comfort if you're an interest group on the receiving end of a broken promise. Immigration activists haven't forgotten Obama's pledge to make immigration reform a top priority in his first years in office, a promise he wasn't able to fulfill.

There's also a difference between general rhetoric and specific promises. There's a difference between Clinton saying things that sound critical of charter schools in a campaign where her major opposition is a candidate more left-wing than she is, and Clinton making a specific promise to pursue policies in line with those views.

Campaign promises are very successful at tying politicians' hands, and signing pledges for outside groups — such as a promise not to raise taxes — is the most successful of all, two political scientists at Stanford, Michael Tomz and Robert Van Houweling found in research on political positioning published in 2012.

But if candidates avoided making specific promises, it was to their advantage. Voters didn't mind it when candidates were vague — in fact, particularly when the candidates were members of their own party, they preferred it.

"We find strong evidence that voters punish candidates for changing position, but do not punish—and sometimes reward—candidates for remaining vague," Tomz and Van Howeling wrote.

The lesson for politicians is clear: The best way to avoid having to keep your promises is to not make any in the first place.