Former Bush campaign strategist Karl Rove explains for Wall Street Journal readers why the electoral map shows that some Senate Democrats’ political prospects are in danger.

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%.