Sen. Lisa Murkowski (R-Alaska). (Andrew Harnik for The Washington Post)

Somewhere between Alaska and West Virginia, there’s an invisible line dividing the Republican Party.

Not literally, of course — or, for that matter, even figuratively. But in the highly contentious battle over whether the Senate should move forward in its pursuit of an overhaul of Obamacare, the ideological gulf between Republican Sens. Lisa Murkowski (Alaska) and Shelley Moore Capito (W.Va.) was what separated a “yes” from a “no.”

The “motion to proceed” vote was decided when Vice President Pence broke a 50-50 tie on Tuesday, a tie that resulted from two Republicans joining 48 Democrats and the Senate’s two independents to stop the health-care bill (or, really, the concept of a bill) from moving forward. Those two Republicans were Murkowski and Sen. Susan Collins (R-Maine), the two most moderate members of the Republican caucus according to data compiled by

Visually, it looks like this. The higher the dot, the more conservative the senator. Dots farther to the left mark senators who represent states that backed Hillary Clinton last year by a wide margin; those farther to the right backed President Trump.

The line we’re talking about is the dashed one running horizontally between the black Murkowski dot and the red Capito one — “the split.” Every senator under that line voted no. Every senator above it voted for the motion to proceed.

Capito seemed like she was likely to vote no until Tuesday morning. A week ago, she publicly declared her opposition to pressing forward without a bill she could support. When push came to shove, that promise fell by the wayside. That her dot is so far to the right might help explain why: West Virginia was a fervently pro-Trump state in 2016, unlike, say, Maine. But, then, her fellow senator, Joe Manchin III — the uppermost dot/most conservative of the Democrats — voted no.

Also highlighted are three senators whose votes seemed particularly important on Tuesday. Nevada’s Dean Heller had publicly wavered on backing the Republican bill; he voted with his party. Sen. Ron Johnson (R-Wis.) was one of the final two senators to vote, playing coy with the media and then casting a yes, as could have been predicted. Likewise John McCain (R-Ariz.) who cast the other of the last two votes. Each of those three senators are from states that voted fairly purple last year, but ideologically, they were more in line with the rest of their caucus than were Collins or Murkowski.

We don’t know that the split line itself is particularly important or wedded tightly to the result of the vote. But we will note that the number of Republican senators as moderate or more moderate than Murkowski is lower in the past three congresses than at any point prior, with most of the party’s caucus being at least as conservative as or more conservative than Capito. A similar vote in past congresses, we might assume, would have yielded much different results.

Where the line may become important is once the Senate figures out what it’s actually voting on. Nearly any legislation that will be offered will end up offering a more conservative choice than simply whether to proceed with debate. In other words, the line will theoretically move up. Will Capito still back it? Will McCain, after offering hints on Tuesday that he might not? This is where other factors come in — Heller’s 2018 reelection, for example, or that pro-Trump fervor in West Virginia.

In this first vote, though, the line fell in just the right place for Senate Republicans to claim victory. As the president put it in an interview with the Wall Street Journal on Tuesday afternoon:

“It’s a very, very difficult situation,” he said, “because you move a little to the left, and you lose four guys. You move a little bit to the right, and all of a sudden you have a bloc of people who are gone. You have a one-inch road and it wheels through the middle of the valley.”

On Tuesday, that road actually ran somewhere between Juneau and Charleston.