We wrote last week about a growing movement in the Republican Party to change how key states award their electoral votes — changes that could have a dramatic impact on how presidential elections are decided. This week, we had our first official movement on that front, with a subcommittee in the Virginia state Senate advancing a bill that would award the state's electoral votes by congressional district rather than on a winner-take-all basis. In light of this, we are reposting our item from last week, with a few updates:

Republican National Committee Chairman Reince Priebus voiced some support this month for an effort to reform how some states award their electoral votes.

And the effect of the movement in helping Republicans win presidential elections should not be underestimated.

Below, we take you through the particulars of the effort, what it would mean, and why it will or won't happen.

What's on the table?

Basically, Republicans who have control of states that went for President Obama in the 2012 election are pushing for their states to change how they award electoral votes. While almost every state awards electoral votes on a winner-take-all basis, Republicans want these states to instead award one vote to the winner of each congressional district.

The other two electoral votes that each state has would likely would be given to the statewide winner, as they are in the two states that currently employ this method: Maine and Nebraska.

The new system would allow Republicans to consistently win electoral votes (and quite possibly a majority of electoral votes) from states such as Florida, Michigan, Ohio, Pennsylvania, Virginia and Wisconsin, regardless of whether they win the statewide vote.

All six of these states went for Obama in 2012. Michigan, Wisconsin and Pennsylvania have consistently gone blue at the presidential level, and Virginia is tilting in that direction, which would make winning any electoral votes in these states a victory for the GOP.

Why does it matter?

It matters because the congressional district method gives the GOP a much better chance of winning, since a strong majority of U.S. congressional districts lean Republican.

The numbers are stark: If every state awarded its electoral votes by congressional district, Mitt Romney would have won the 2012 presidential election despite losing the popular vote by nearly four percentage points. According to Fix projections and data from Daily Kos Elections, Romney won at least 227 congressional districts and 24 states, giving him 275 electoral votes — more than the 270 he needed.

In fact, Romney would have won last year even if just the six states mentioned above changed their systems. Despite losing those six states, Romney won 64 of their 104 congressional districts, and adding 64 electoral votes to his total of 206 would have given him exactly the number he would need to win the election — 270.

The six states mentioned above are the most important because Republicans drew their district maps in 2011 and 2012, and they drew very favorable maps on which they are likely to dominate for the next decade or longer.

Why it could happen

Despite their 2012 losses, Republicans continue to hold control of the state legislature and the governor's mansion in all six states. That means, with enough political will, they may be able to push through such changes.

Republicans also have a window of opportunity right now. Over the next two years, they will have to defend the governor's mansion in all six states, and their majorities in some of those state legislative chambers are going to be at risk as well, so now may be their last shot. In addition, such changes are best made as far away from the next presidential election as possible, in hopes of avoiding a backlash over gaming the system.

Republicans wouldn't have to worry much about Democrats doing something similar — at least not right now — in response. That's because Democrats don't hold full control over the state government in any red state except West Virginia.

Why it wouldn't happen

First, making something like this work is tricky politics. It's pretty clear that Republicans are looking at these changes for political gain, rather than because they make sense as reforms, and voters may not like that. (There's a reason the GOP is proposing this in blue and swing states they control rather than red states they control, because in the latter case they would be losing electoral votes.)

Secondly, with Govs. Tom Corbett (R-Pa.), Rick Snyder (R-Mich.), John Kasich (R-Ohio), Scott Walker (R-Wis.) and Rick Scott (R-Fla.) already having dealt with some very tough issues in their tenures and having the political scars to show for it, there may not be an appetite for something so difficult and uncertain.

And thirdly, congressional districts change every 10 years, so who is to say that the changes wouldn't one day hurt the GOP? And what if states like Wisconsin or Michigan one day tilt red? Then Republicans would prefer them to be winner-take-all again.

History suggests that such a change would have favored Republicans in basically every close race over the past half-century — and often in a significant way — but with any big change comes unintended consequences.

Priebus, in announcing his openness to the push, emphasized that the change would create greater "local control," and an argument could be made that it would encourage presidential candidates to pay closer attention to their states. It's also notable that two states are doing the congressional district method, so it's not like this is a totally outside-the-box idea.

But it's still a tough argument to make.