Momentum and Field Position

Political momentum is hard to define, though I know it when I see it. Instead let me offer a couple of football metaphors: field position and takeaways.
In terms of field position, most of the seats considered in play by knowledgeable observers are held by Republicans. Only one Democratic Senate seat is in play, that of Bob Menendez in New Jersey. In contrast, Democrats are likely to pick up Republican seats in Rhode Island, Pennsylvania, Ohio and Montana.
You thought Ohio was more of a toss-up? So did I. But the New York Times reports that Sherrod Brown is now clearly ahead of incumbent Mike DeWine:

The Democratic candidates for governor and Senate hold commanding double-digit leads over their Republican opponents in the poll, and respondents said they intended to vote for the Democratic candidate for the House in their district by 50 percent to 32 percent.

As for CQPolitics.com, this is another race that it has changed to Leans Democratic:

In DeWine’s case, a one-two punch of independent polls showed his Democratic challenger, seven-term Rep. Sherrod Brown, leading by significant margins — 7 percentage points in one survey and 12 in the other.
This is a breakthrough for Brown, who is running on a liberal-leaning but populist economic platform and his strong opposition to President Bush’s policies on the war in Iraq. Though Brown has led in most polls since the summer, his leads previously tended to be within the statistical margin of error.

And speaking of moving the ball deep into the opponent's territory, in Montana Jon Tester is favored to win against the hapless, and scandal tainted, Conrad Burns. Tester, who was once considered a long shot, exemplifies the progress Democrats have made as a national party.
Consider: Tester is leading in Montana even though he opposes the Patriot Act, and isn't afraid to say so, as in this TV ad posted over at DailyKos, that asks of Burns, "Why do you think we're the enemy? Where's Osama bin Laden? And when did you get so out of touch with Montana?"
Turning to the House, Larry Sabato's Crystal Ball rates 16 races in the Toss-Up category; not one is held by a Democrat. He also has 11 GOP seats in his Leans Democratic category. Sabato's analysis, released October 12, reveals the extent to which Democrats are playing on the Republican end of the field:

In fact, to reflect just how precipitously many GOP-held seats have drifted from safe harbor, we have had to jettison not only the "Dirty Thirty" but now the "Ferocious Forty" as well. In their place, meet the "Ferocious FIFTY" theaters of battle, 42 of which are currently held by Republicans.

Look for his next analysis to shift even more sharply in the Democrat's favor.
I suggest a second metaphor, takeways, to describe those Republican seats that are simply being fumbled away. As Sabato wrote back on October 5, "this year, the GOP has been giving away seats in Congress as if they were extra pairs of upper-deck Washington Nationals tickets." Tom DeLay's district in Texas, Mark Foley's Florida district, Tom Reynolds' New York district -- none of which were thought to be in play at the beginning of the year -- are likely to change hands due to scandals.
With Democrats pulling ahead in the close races, and favored to win seats they have no business even contesting in a normal year, there is little question that we see a big shift coming in Congress.