Three sets of numbers have emerged in recent weeks that bode ill for Democratic hopes to keep the U.S. Senate. The first came from new Federal Election Commission filings and news reports on campaign fundraising for the fourth quarter of 2013, and cash-on-hand on Dec. 31.
Seven states carried by Mitt Romney have Democratic senators whose seats are up in November. Overall in these states, the leading Republican candidates raised $6.5 million while their Democratic opponents—including four incumbents—raised $6.7 million during the last quarter. Five Republicans outraised their Democratic opponents, including in all three states (Montana, South Dakota and West Virginia) where the Democratic senators are leaving and in two of the four states (Alaska, Arkansas, Louisiana and North Carolina) where Democratic incumbents are trying to hold on.
Republicans also whittled away at the Democratic cash-on-hand advantage in these states. Democrats had an $18.5 million to $11.5 million cash advantage at the end of September. By the end of December, Democrats had roughly $21 million, Republicans $15.5 million.
The second troubling number for Democrats is Gallup's presidential job-approval rating, which was 42% the week ending last Sunday. The president's average approval in these seven Senate states is roughly 36%. If that's the case on Election Day, he will likely sink his party's candidates, who probably cannot run more than five points ahead of Mr. Obama's rating.
Then there is the nonpartisan Congressional Quarterly's summary of last year's legislative voting patterns. The four red state Democratic senators running for re-election gave Mr. Obama's policies almost perfect support, led by Louisiana's Mary Landrieu and Alaska's Mark Begich at 97%, followed by North Carolina's Kay Hagan at 96% and Arkansas's Mike Pryor at 90%.
They are now trying to distance themselves from the president. Mr. Begich says he's "disappointed" in the State of the Union address and promises to "push back" if Mr. Obama signs objectionable executive orders. But Dan Sullivan, the former Alaska Natural Resources Commissioner and the likely Republican candidate, can make hay all day long with the senator's voting record.
Ms. Hagan refused to appear with Mr. Obama when he visited North Carolina Jan. 15. Her likely GOP opponent, state House Speaker Thom Tillis, can cite this to show that she was rock-solid reliable when it came to advancing the Obama agenda but now that she has to face voters, she's ashamed.
These problems—a diminishing fundraising edge, low presidential approval, and support for Mr. Obama's policies—could cause problems for Democratic senators in purple states as well. In 2010 Republicans picked up six Senate seats (the number they need this year to win control). Five were in states Mr. Obama carried in 2008, namely Florida, Illinois, Ohio, Pennsylvania and Wisconsin.
Four purple states already appear promising for Republicans. In Michigan, Republican Terri Lynn Land has outraised Rep. Gary Peters, her Democratic opponent, the last two quarters. Despite his five-year head start in building a war chest, Ms. Lynn now has more cash ($3.3 million versus $2.9 million). Mr. Peters also supported Mr. Obama's policies 90% of the time in 2012, the most recent year available for House members.
In New Hampshire, Democratic Sen. Jeanne Shaheen supported Mr. Obama's policies 99% of the time in 2013. While she has $3.4 million, what happens if former Massachusetts Sen. Scott Brown —a New Hampshire native who now lives in the Granite State—runs? He raised $28.2 million for his last campaign.
Minnesota Sen. Al Franken supported Mr. Obama's policies 100% of the time last year and Virginia Sen. Mark Warner backed them 97% of the time. Both could face Republican challengers—businessman Mike McFadden in Minnesota and former GOP National Chairman Ed Gillespie in Virginia—who can raise money and could take advantage of Mr. Obama's unpopularity in their states. Other purple possibilities that could develop are Oregon, New Mexico, Colorado and Iowa.
Today the GOP has seven Democratic seats clearly in play and several more shaping up. If Republicans can increase that to 10 Democratic seats, their chances of regaining Senate control and providing an important institutional check on Mr. Obama's agenda during his last two years go up dramatically.
A version of this article appeared February 6, 2014, in the U.S. edition of The Wall Street Journal, with the headline The Numbers That Scare Senate Democrats and online at WSJ.com.