ABC News Race Ratings Show Tight Race for Control of US Senate

— -- With several vulnerable Republican seats up for grabs in the U.S. Senate in the 2016 elections, the two major parties are locked in a tight battle for control of Congress’ upper chamber this November.

ABC News ratings show control of the Senate will be a close contest in November: Republicans will likely finish with at least 47 seats and Democrats likely with 47 seats — with the six remaining seats rated as pure toss-ups.

Many of the seats the GOP won during the 2010 tea party wave are now up for re-election, so holding on to its 54-seat majority was always going to be a tall order for the GOP.

But with competitive seats in battleground states like Florida and Ohio leaning red and seats in states like Pennsylvania and New Hampshire remaining tight, control of the chamber is very much in question as we head into the final weeks of the campaign.

Senate terms are for six years, and one-third of the seats come up for election every two years, so 66 seats — 30 Republican and 36 Democratic — are not in contention this year.

Fifteen seats are rated solid Republican, versus ten that are solid Democratic. Two seats are leaning Republican, one seat is leaning Democratic, and six are toss-ups.

Solid RepublicanAlabama, Alaska, Arizona, Arkansas, Georgia, Idaho, Iowa, Kansas, Kentucky, Louisiana, North Dakota, Ohio, Oklahoma, South Carolina, South Dakota, Utah

Leans RepublicanFlorida

Toss-upIndiana, Missouri, Nevada, New Hampshire, North Carolina, Pennsylvania, Wisconsin

Leans DemocraticNone

Solid DemocraticCalifornia, Colorado, Connecticut, Hawaii, Illinois, Maryland, New York, Oregon, Vermont, Washington

U.S. House of Representatives

The race for control of the House of Representatives is tightening, with a number of districts across the country evenly in play. Republicans currently hold a 30-seat advantage, 246 to 186, with three vacancies — likely enough to hold on to the chamber into 2017 and shape legislative action regardless of the fate of the Senate or the White House, but Democrats are pushing closer in our most-recent ratings.

ABC News gives an advantage to Democrats in six seats currently held by Republicans and rates 17 additional races as a tossup. Even if Democrats sweep those races and protect the one Democratic seat that is rated as turning red, the party would still need an additional eight seats for a majority.

The GOP has a solid hold on 203 seats, versus 180 seats that are solid Democratic. An additional 23 seats are leaning Republican, 12 seats are leaning Democratic, and 17 are toss-ups.

Ratings Changes

Nov. 4: A Marquette University poll this week showed the Wisconsin Senate race as a dead heat, with Russ Feingold at 45 percent and Johnson at 44 percent support. Both sides have continued to pour money into the state over the last several weeks, including $2.2 million from the GOP-linked Senate Leadership Fund for advertising and get-out-the-vote efforts and $2 million from the Democrat-linked Senate Majority PAC. And recent polling showing Trump remaining competitive there bodes well for Republicans down ticket, who have tended to run slightly ahead of him.

Two new polls in Arizona show incumbent Sen. John McCain holding a broad, double-digit lead in Arizona. An NBC/WSJ/Marist poll this week shows him leading 55-39 percent and a CNN/ORC poll shows him ahead 54-41 percent. Early voting originally had showed Democrats turning out above expectations, but Republicans now lead, according to data from state election officials. The former 2008 GOP nominee is expected to defeat Democratic challenger Ann Kirkpatrick.

Additionally, the Southern California district of Rep. Darrell Issa, the former Chairman of the House Oversight and Government Reform Committee who polls show locked in a difficult bid for reelection, is now rated as a Tossup.

Oct. 28: Senate seats in both Ohio and Illinois moved from Leaning to Solid this week, but on opposite sides of the aisle. Sen. Rob Portman of Ohio appears to be in good position to retain his seat and Rep. Tammy Duckworth has firmly taken control of her race to unseat incumbent Sen. Mark Kirk in Illinois.

Only one change was made to the house of representatives this week: Iowa's 1st congressional district, held by Republican Rep. Rod Blum, is now a Tossup. It was previously rated Leans Democratic.

A number of house districts shifted to the left in the most recent ABC News race ratings update. From the last update, two solid Republican seats were downgraded to leaning Republican, five leaning Republican seats were downgraded to toss-ups, and one toss-up shifted to leaning Democratic.

Oct. 21: A number of house districts shifted to the left in the most recent ABC News race ratings update. From the last update, two solid Republican seats were downgraded to leaning Republican, five leaning Republican seats were downgraded to toss-ups, and one toss-up shifted to leaning Democratic.

Senate ratings did not change.

Oct. 14: ABC News has changed the rating in the race between incumbent Missouri Sen. Roy Blunt and Democratic challenger Jason Kander from leaning Republican to toss-up. Democrats have shifted resources to the state after races in Ohio and Florida began to appear out of reach. Polling shows a competitive race and operatives on both sides continue to invest resources there. The House of Representatives ratings remain unchanged.

Oct. 7: ABC News has changed the rating in the race between incumbent North Carolina Republican Sen. Richard Burr and Democratic challenger Deborah Ross from leaning Republican to toss-up. Polling in the state in the continues to show that Tar Heel State voters are relatively evenly split in all three major races in the state: the senate, gubernatorial and presidential elections.

In the House of Representatives ratings, solid Republican seats dropped one, from 206 to 205, while solid Democratic seats remained unchanged at 178. Leaning Republican seats increased from 22 to 27, and leaning Democratic seats jumped up one from 13 to 14. The number of toss-up seats declined as a result, falling from 16 to 11.

ABC News’ John Kruzel contributed to this report.