For much of the year, we've been talking about the GOP potentially winning the Senate. For that entire time, though, Republicans as a party continued to trail in polls pitting them against Democrats -- a common polling question known as the generic ballot.

That changed this week.

The Pew Research Center on Friday became the sixth straight national poll to show Republicans taking a lead on the generic ballot (by three points, 47-44). Earlier in the week, a Washington Post-ABC News poll showed the GOP up three, a CNN poll showed it up four, and a Fox News poll showed it up seven.

As you can see below (with an assist from HuffPo Pollster), this is the first time all year that Republicans have shown a clear lead in the lion's share of generic ballots -- much less all of them -- for a significant period of time.

A big part of the reason for the GOP's newfound edge, as we've discussed before, is that pollsters are switching from testing registered voters to likely voters. The new Pew poll, for instance, shows the GOP trailing by five points among registered voters, even as it leads by three among likely voters. Our WaPo-ABC poll this week also showed the GOP down two among registered voters.

This is because Republican voters, in general, are more likely to turn out both in midterms in general and in this particular midterm, in which they are more motivated than Democrats.

But it's also worth noting that even the limited likely-voter samples conducted throughout the year largely showed a close race or Democrats leading.

And even if the shift is mostly about the new likely-voter samples, it's still good news for Republicans; after all, this is the electorate we're expecting to show up. And it's generally acknowledged that a neutral environment is when the GOP is trailing by a few points on the generic ballot, so any kind of a lead is notable.

But it's also not quite as big a lead as they had in 2010, when they led the generic ballot by six points on the eve of the election. They had also, by this point, been showing a big lead on the generic ballot for a long time. So, clearly, the advantage isn't as baked-in this time around.

Should they continue to build a generic ballot lead, though, get ready for a big GOP year.