According to recent polling, Democratic candidates are making major gains key Senate races across the country.

In Massachusetts, Democrat Elizabeth Warren has surged ahead of incumbent Republican Scott Brown in four polls that were released this week. Public Policy Polling has Warren leading Brown by a 48 to 46 percent margin, Western New England University’s Polling Institute has Warren leading 50 to 44 percent, Suffolk University/WHDH-TV has Warren leading 48 to 44 percent, and WBUR has Warren leading 45 to 40 percent. Brown did lead Warren 50 to 44 percent in a UMass Lowell/Boston Herald poll released on Thursday, but aside from that poll, Warren is trending quickly upwards.

The Senate race in Virginia appears to be shifting towards the Democrats as well. Former Governor Tim Kaine leads former Senator George Allen in two polls released on Wednesday. A Washington Post poll shows Kaine with a 51 to 43 percent lead, and a Quinnipiac/New York Times/CBS News poll shows Kaine leading 51 to 44 percent. These results represent a dramatic shift in Kaine’s favor — until this week, the race had been essentially tied all year.

In Wisconsin, two recent polls show Democratic Rep. Tammy Baldwin rapidly gaining ground in her race against former Governor Tommy Thompson. On Wednesday, a Quinnipiac/New York Times/CBS News poll had Baldwin and Thompson tied at 47 percent; this is a six-point swing from their previous poll, which gave Thompson a 6 percent lead at the end of August.

A Marquette Law School poll released Wednesday shows an even greater surge for Baldwin. According to the poll, Baldwin leads Thompson by a 50 to 41 percent margin, easily marking her biggest lead of the campaign so far.

Finally, in Arizona, a poll released on Wednesday night shows Dr. Richard Carmona leading Republican Rep. Jeff Flake by a 44 to 39 percent margin. Although Flake is still widely favored to win the race, the poll confirms that Carmona has a very real chance of stealing what was initially considered to be a safe Republican seat.

Taken together, these polls are a serious red flag for the GOP. Republicans must win a net total of three seats to control the Senate if Mitt Romney wins the presidency, or four seats if President Obama is re-elected. If Democrats win even two of the above races, then that task will become virtually impossible.

New York Times statistician Nate Silver doesn’t like the Republicans’ odds. Silver now projects that the Democrats have a 79 percent chance of holding a majority in the Senate, up from just 38.5 percent one month ago.