While campaigning in Colorado in July, Donald Trump proclaimed, “We have to win this state.” The statement might have seemed at the time to be little more than political boilerplate, given that the state boasts only nine electoral votes. As it turns out, the Republican presidential nominee was right.

Presidential election prognosticators typically look at voting patterns in three key states — Ohio, Pennsylvania and Florida — in predicting election outcomes. In the past 13 elections, the candidate who managed to take at least two of these states ended up winning the election. This pattern is in jeopardy of being broken this year, making Colorado potentially the most important electoral state.

To see why Colorado will loom so large in this election, let us consider the following hypothetical electoral scenario. Let us assume that Trump will win every single state where he is currently leading and all states that he has a reasonable shot at winning (where he has consistently polled within three points of Clinton). These states include Arizona, Georgia, Iowa, Nevada, North Carolina and, most importantly, Ohio and Florida.

To be sure, it is a long shot that he will indeed win all of these states, but remains within the realm of possibility. Capturing all of these states puts Trump’s total number of electoral votes at 265, five short of the number needed to clinch the election. This means that Trump must not only capture all of the states mentioned above, he must also flip at least one “blue” state.

There are six possibilities: Pennsylvania, Wisconsin, Michigan, New Hampshire, Virginia and Colorado. Trump has little to no chance of winning the first four. Not only does Clinton enjoy sizable leads in each of them, but over the past six election cycles, these states have voted for Democratic presidential candidates 23 times and the Republican candidate only once (New Hampshire in 2000).

Virginia might seem a likely state to be flipped, considering that it has voted Republican 10 out of the past 12 elections. The problem, however, is that demographic changes over the past decade appear to have turned Virginia into a solidly blue state. President Obama was to capture the state in both the 2008 and 2012 elections. Furthermore, of all the swing states, polls show that Clinton enjoys her largest lead in Virginia. No poll over the past three months shows Clinton trailing Trump in Virginia. If Clinton can capture all five of these states, then she will find herself with 264 electoral votes to Trump’s 265.

This brings us to Colorado. Polling in September shows that Trump narrowed Clinton’s lead in Colorado significantly, although a Monmouth poll released Monday showed her up 11 points. Historically, Colorado has a more ambivalent voting record than the other five possibilities. In the past six presidential elections, Republicans and Democrats have each won the state three times. For these reasons, Colorado appears to be the state most likely to flip from blue to red this election cycle.

It is quite possible, of course, that Clinton could take Ohio, Florida, North Carolina or Iowa from Trump, rendering Colorado irrelevant. But this is far from a foregone conclusion, given that Trump is currently either virtually tied with or enjoys a slight lead over Clinton in all four states. The point, however, is that even if Clinton can win the election without capturing Colorado, Trump cannot. For this reason, a win for Clinton in Colorado could likely be what lands her in the White House.

Nilay Saiya is an assistant professor of political science and director of international studies at the State University of New York, Brockport.

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