* Cook Political Report…

The last two weeks have seen some significant movement in Democrats favor. First, there were the impressive results from last Tuesday’s elections. This week, we’ve seen two polls — one by Quinnipiac and one by Marist — that show Democrats with a congressional ballot advantage of +13 to +15. Three other recent polls — ABC/Washington Post, Fox, and NBC/Wall Street Journal — show Democrats with an advantage of anywhere from +7 to +15.

These are political wave numbers. […]

My colleague David Wasserman has been digging into the question of just how big of a wave Democrats need to get in order to surf into the majority. The short answer: they need to see a generic ballot advantage of +8 or more, which roughly translates to getting at least 54 percent or more of the national House vote in 2018.

The last time Democrats enjoyed a margin of +8 or more in a mid-term year was 2006. That year, Democrats won the House vote by 8.5 percent. The last time that Democrats got into the double digits was 2008 when they carried the House vote by D+11. This has led to a lots of talk that Democrats can only hit significant margins of victory in presidential elections when their base is more engaged and involved. It also helped to have a transformational candidate - Barack Obama - at the top of the ticket. Something they obviously don’t have in 2018. But, there is precedent for Democrats winning the House vote by double digits in mid-term years. In the post-Watergate midterm of 1974, Democrats won by a whopping 17 points. In Ronald Reagan’s first midterm of 1982, Democrats won the House vote by 12 points.

* As a result, Cook has moved Peter Roskam from “Lean Republican” to “Toss Up”…

IL-06: Peter Roskam (R) - Chicago west suburbs: Wheaton, Palatine

Toss Up. Roskam has been a party loyalist since 2006, narrowly losing a bid for GOP whip in 2014 and casting conservative votes. But his suburban Chicago district has moved away from the GOP so fast that Democrats are now wishing they hadn’t protected him in their 2012 gerrymander. In 2016, Clinton won this seat 50 percent to 43 percent. Only eight House Republicans represent a seat Trump lost by more. Defeating Roskam will be Chicago Democrats’ top priority.

The large Democratic field is led by financial adviser and former North Barrington Village Trustee Kelly Mazeski, who had $343,000 on hand at the end of September. Clean energy businessman Sean Casten, former congressional aide Carole Cheney and 2016 nominee Amanda Howland are running too. Fortunately for Democrats, Illinois’s March 20 primary should give the nominee more time to consolidate support and raise money to compete in a very expensive market.

…Adding… I’ve generally avoided covering the Dem primary because there are so many hopefuls and I wasn’t sure who would even survive the petition season. This may change things…