Unlike hypothetical polling — Who might you vote for in three months? — the launch of early voting means pollsters can survey which candidate is actually stacking up more ballots. Sen. Barack Obama has the early lead.

The Obama campaign has prioritized early voting in key states like Nevada. (Credit: Obama Flickr)

Pew reports today that among people who say they have already voted, Obama has a 19-point lead.  That’s not a small cohort either; 15 percent of those surveyed say they have already voted.

Another 16 percent say they plan to vote early — and Obama leads that group by 19 points too.

The poll also has numbers on the candidates’ current hypothetical support, as TWI’s Aaron Wiener reported earlier. Obama’s 16-point edge is far less relevant than the early-vote margins, of course, though Pew’s analysis emphasizes a trend of McCain’s support  eroding and Obama’s holding strong among those most likely to turn out next Tuesday:

This is the fourth consecutive survey that has found support for the Republican candidate edging down. In contrast, since early October weekly Pew surveys have shown about the same number of respondents saying they back Obama. When the sample is narrowed to those most likely to vote, Obama leads by 53% to 38%.

Out of habit, we often discuss (and report) the campaign as a countdown to a single day of voting, but that’s obviously inaccurate.  The voting has begun, the exit polling has begun and for the first time, Obama has a lead that actually matters.

On Iraq, McCain led by seven points in early September, 48%-41%, but now it’s Obama with a six-point advantage, 48%-42%

And no, this wasn’t a poll of Iraqis.