While the Republican candidates for president are tearing their hair out trying to figure out how they can deal with a bizarrely formidable Donald Trump, Hillary Clinton has the luxury of rolling out policy ideas on her own schedule. This week she debuted another one: an ambitious increase in the nation's supply of renewable energy, meant to make a dent in American carbon emissions. In keeping with her previous policy proposals, there's plenty to please liberals. But there are real questions about how she'd go about achieving her goals.

The Clinton campaign says it will be rolling out her climate plans in stages; this first part is about clean energy. Clinton proposes to increase the nation's solar capacity by 700 percent by 2020, and to generate enough renewable energy by 2027 to power every home in America. As Brad Plumer points out, electricity generation accounts for only 38 percent of carbon emissions, so that doesn't solve the whole problem, but it's still an extremely ambitious goal.

The details on how to get to that goal are thin at this point — a "Solar X-Prize," tax incentives, use of public land for renewable energy generation — but the real question may be not whether you could devise a specific plan to get there, but whether such a plan could be put into action. No matter how serious Clinton is about this issue, as president she'd face an uphill climb.

That's partly because the Obama administration has already taken many of the executive actions readily available to deal with climate change. The administration set ambitious new fuel efficiency standards for cars, capped carbon emissions from power plants (limits that Clinton has said "must be protected at all costs"), and struck a deal with China to reduce carbon pollution. It is readying a new round of regulations on emissions from airplanes, trucks, and oil and natural gas operations. It just announced that it had recruited major corporations like Microsoft, General Motors, and Walmart to pledge to reduce their carbon emissions. And that's not to mention the fact that the 2009 Recovery Act (aka the stimulus) was, among other things, the largest clean energy bill in American history.

There are plenty of climate hawks who say that while this record is pretty good, it pales before the magnitude of the challenge. Which is probably true. But it also means that Clinton will have be creative if she wants to go far beyond what the Obama administration has done, particularly through regulation.

The other reason this is a challenging issue for Clinton is that she'll likely be facing a Republican Congress if she's elected president. Although significant numbers of Republican voters accept the reality of climate change, the default position for politicians in the party is that while the planet may or may not be getting warmer, we certainly shouldn't do anything about it. Of the 16 Republicans running for president, only one — Lindsey Graham — actually thinks it's an issue worth addressing. The positions of the rest of them range from "I'm not a scientist" to "It's a big hoax."

The Republicans in Congress are no better. If a President Clinton were very lucky, she might have a Democratic Senate to deal with, but she'll still certainly face a Republican House. That means that the likelihood of significant climate legislation reaching her desk is near zero. Most of what she's proposing would require legislation. How is she going to get Republicans to agree to it?

Of course, that's a question that hangs over anything Clinton (or any other Democrat) proposes. Perhaps it's not fair at this point to demand an answer — we can start by learning exactly what she'd like to do, and then we can figure out whether she can do it. But when you're talking about an issue like this one, where resistance from Republicans will be strong, it's impossible to avoid.

On the other hand, maybe Republicans will join with a President Clinton to safeguard the planet's future — especially when doing so could produce untold numbers of jobs and a variety of other benefits to the economy and Americans' health. Probably not, though.