Mitt Romney concludes a five-day bus tour through six swing states with a stop in his homestate of Michigan today, a trip that speaks volumes about how the former Massachusetts governor views his path to 270 electoral votes this fall.

Romney began his tour in New Hampshire and has made subsequent stops in Pennsylvania, Wisconsin, Iowa, Ohio and, today, Michigan. (Worth noting: Romney has drawn largely favorable press out of the bus tour; he and his team have to be happy with the “Mitt Romney receives newfound enthusiasm from Republicans” in today’s Washington Post, for example.)

Those six states were all carried by President Obama in 2008. In fact Obama averaged nearly 55 percent of the vote in the six states combined. Those six states award 72 electoral votes, roughly 25 percent of the total either Romney or Obama need to be elected president.

As we have written before, President Obama starts with an edge in the map with 196 electoral votes solidly in his camp as opposed to 170 solidly for Romney. (That disparity is largely due to the fact that major population states like California, New York and Illinois are all heavily tilting toward Obama).

What’s clear from this bus tour — and, make no mistake, these six states were not chosen at random by the Romney campaign — is that the former Massachusetts governor and his team believe that their path to the presidency goes through this sextet of states.

Let’s follow the Romney map — and the math.

Start Romney at 170 solid electoral votes. Add in Arizona and Missouri — two states leaning toward Romney — and he is at 191 electoral votes. Put North Carolina, which we currently rate as a “toss up” but where nothing seems to be going right for the Obama team of late, and Romney is at 206. Add Florida, a state that still looks like a toss up but where Republicans are quite confident of their chances and he is at 235 electoral votes.

That’s where the six states Romney is currently touring on a bus (and a plane) come in.

Win just 35 of the 72 electoral votes offered by those six states and Romney is the next president of the United States. That is by no means an easy task — but neither is it unimaginable.

The must-have-state for Romney — as expertly explained by the Post’s Dan Balz on Monday — is Ohio (and its 18 electoral votes). President George W. Bush won the state twice and Republicans scored across-the-board victories in the Buckeye State in 2010, winning the governorship and an open U.S. Senate seat.

Iowa and New Hampshire seem the two next most likely to fall for Romney as Bush won Iowa in 2004 and New Hampshire in 2000. (He might well have won New Hampshire in 2004 as well but Massachusetts Sen. John Kerry had a geographic connection to the Granite State.)

Give Romney Ohio, Iowa and New Hampshire and he is at 263 electoral votes — just seven shy of the mark.

The three remaining states — Michigan, Wisconsin and Pennsylvania — award 46 electoral votes but none of them are easy sledding for Romney. No Republican presidential candidate has carried any of the three states since 1988 and since that time the GOP nominee has averaged 42 percent (Michigan), 43 percent (Pennsylvania) and 44 percent (Wisconsin).

Of the three, Wisconsin seems like Romney’s best chance as Bush came within .4 percent of winning the Badger State in 2004 and the recall victory of Gov. Scott Walker last month has emboldened conservatives nationwide.

Pennsylvania would be next on that list — although Democrats roll their eyes when Republicans talk about winning the Keystone State. (The comparison of Charlie Brown trying to kick the football and Lucy pulling it away is often cited.) Still both sides are spending money in the state — and no campaign or outside group spends money if they don’t think that a state is at least marginally up for grabs.

While Michigan is Romney’s home state — his father served as the governor — it is a very tough state for Republicans to win. Yes, Rick Snyder was elected governor in 2010 but that was in reaction to eight years of an unpopular Democratic governor and a Democratic state party in shambles (or close to it).

Win any one of those three states, however, and Romney is president. Or lose all three and win Colorado. Or Virginia.

To be clear: Obama still has more paths to 270 electoral votes than does Romney. But, if — and it’s a big if — Romney can win three of the states he has spent time in this week (Ohio, Iowa and New Hampshire) and pick offone of the other three (Wisconsin, Michigan and Pennsylvania), his potential paths to victory would multiply greatly.