One of the big surprises on election night this year was the jump in the proportion of the electorate under the age of thirty. Prior to Nov. 6, reputable pollsters consistently reported declines in youth voter enthusiasm and touted evidence that young voters were barely tuned-in to the election process.

The 2008 election was viewed as an aberration, a one-time-only affair where the novelty of an exciting, inspirational candidate swept a whole generation into the voting booths. But young voters didn’t stay home this year. In fact, as a proportion of the electorate, they grew to 19 percent—the highest level in 20 years according to the exit polls.

It appears that despite lower overall voter turnout, young voters turned out in raw numbers equal to 2008—just over 23 million votes cast. And it was these votes that made all the difference.

Some back-of-the-envelope calculation shows that while Mitt Romney actually won nearly 2 million more votes than President Obama nationwide among voters aged 30 and up, it was Obama’s astounding 5.4 million vote advantage among these young voters that handed him his popular vote victory.

Run the same calculations in the swing states and Mitt Romney wins voters aged 30 and up in Ohio, Florida, Virginia and Pennsylvania, but he loses the youth vote by enough of a margin to lose those states and the Electoral College. It’s time for the GOP to stop believing the youth vote doesn’t matter.

There are two key myths that drive the belief that young voters aren’t worth the effort. The first is that they don’t show up. (Hopefully this year’s election has shattered that myth decisively.) Even in an election without Barack Obama on the ticket, young voters have never made up less than 17 percent of the electorate in a presidential year since the voting age was lowered in 1972.

The second myth is that young people “naturally” become conservative as they age, and thus Republicans shouldn’t worry about losing these voters by double-digit margins. What most don’t know is that it hasn’t always been this way.

George W. Bush only lost young voters by two points in 2000, and he actually won young voters in swing states like Ohio and Virginia that year. Even in his reelection, Bush only lost young voters by a nine-point margin nationally. Obama’s 34-point margin among young voters (and 23-point margin in his reelection) is the exception, not the rule.

The real trouble for Republicans is that a young person’s first few elections can influence their voting behavior the rest of their lives. Research has shown that voters who came of political age during the Reagan presidency are still more likely to be Republican to this day than those who are older or younger than them. Similarly, once a voter casts a ballot for one party a few times, they form the habit and brand loyalty to that party that echoes throughout their political lives. Losing young voters today means losing them tomorrow, even when they’re older.

If you look at the 2012 exit polls and compare them to 2008, Barack Obama’s margin of victory among each age group was smaller than four years ago, with one exception: 30-somethings. Among voters aged 30-39, President Obama did slightly better. It’s anyone’s guess why that’s the case, but I have a theory: those older millennials who broke heavily for Obama in 2008 grew up, entered that 30-39 bracket, and continued to vote for the president in large numbers.

Young voters had a major impact on the outcome of the 2012 election. If Republicans want to be competitive in the future, they absolutely need to start the hard work of rebuilding the party’s brand with young people, and to start that work today.

Kristen Soltis Anderson is vice president of The Winston Group, a D.C.-based polling and consulting firm. She serves as the communications advisor to Crossroads Generation and is also a senior fellow at the Independent Women’s Forum.