Mitt Romney's standing in the presidential race has added more uncertainty to the roller-coaster ride Republicans have been on in their quest to control the Senate.
The GOP began the cycle believing the Senate was within its grasp, given the 23 seats Democrats were defending, many of them in states where the GOP expects to thump President Obama.
Hopes dimmed first with Sen. Olympia Snowe’s retirement, which put a safe GOP seat in play in Maine. They flickered again after Obama’s poll numbers rose following the Democratic convention.
Yet polls across the country show Senate GOP candidates trailing or tied with their Democratic rivals in red-leaning states like North Dakota, Missouri and Arizona.
And Republicans awoke Wednesday to worries that comments about pregnancy and rape by Indiana Treasurer Richard Mourdock had endangered that candidate’s hopes of holding a seemingly safe GOP seat.
GOP strategist Matt Mackowiak acknowledged the fight for the Senate has been volatile, and that there have been mood swings for Republicans. But in the end, he said the top of the ticket will make the biggest difference in the race for the Senate.
"There was a time when Republicans felt really good about the Senate,” he told The Hill. “There was a time Democrats felt a lot better, too. Ultimately, the fortunes for a lot of these candidates are going to be dictated by the top of the ticket."
There are now nine toss-up Senate races, according to The Hill's race ratings, and Democrats are seen as having a strong chance at holding the upper chamber. But three of those races — Nevada, Virginia and Wisconsin — are in hotly contested presidential swing states, where most voters will be turning out to vote for the top of the ticket.
A Romney win in those states could trickle down the ballot to boost other candidates, meaning any tiny swings in momentum could flip the race for control of the Senate.
“My guess is whoever has this majority is going to have 51 seats — a really good night for either party would be 52 seats,” said Jennifer Duffy, the Senate editor of the nonpartisan Cook Political Report.
Duffy said that there’s no clear momentum for either party nationally, a big difference from the last three wave elections, so any minor breeze could push a number of Senate races toward one party or the other.
“In any of these races, when we're talking about a little bit of an advantage, we're still talking about within the margin of error,” she said.
A Senate majority, coupled with a Romney victory and the GOP’s continued control of the House, would give Republicans control of two branches of government, and would likely put an end to much of President Obama’s healthcare law.
Republicans were confident they would win control of the chamber a year ago. Democrats were defending many more seats overall, and 11 Democrats were running in swing or GOP-leaning states, while just three Republicans were in that position. Democratic retirements in Nebraska, North Dakota and Wisconsin made them even more bullish.
But Snowe’s decision to retire turned that seat from a GOP slam-dunk to a likely Democratic pickup; Mourdock’s defeat of longtime Sen. Dick Lugar (R-Ind.) in their primary made that race more challenging; and Rep. Todd Akin’s (R-Mo.) comment that “legitimate rape” rarely leads to pregnancy hurt his campaign against Sen. Claire McCaskill (D-Mo.) in a seat Republicans once expected to pick up.
When Romney hit his own nadir with his comments that 47 percent of the nation saw themselves as “victims” who are “dependent on government,” some Democrats predicted they would not only hold the Senate but keep the same amount of seats.
But Romney has recovered in recent weeks, and so have some Republicans. His improving numbers in Virginia are helping former Sen. George Allen (R-Va.), who’s running a close race with Democrat Tim Kaine. Allen will likely run a few points behind Romney in the state; thus, a Romney win there could net the GOP a Senate seat.
Former Wisconsin Gov. Tommy Thompson (R), who had slipped behind Rep. Tammy Baldwin (D-Wis.) in the polls, has now caught up with her as Romney’s numbers have improved in the state. Thompson will likely run slightly ahead of Romney, so if things stay close at the presidential level, his odds improve dramatically. A Thompson win would add another seat to the Republican column.
In Nevada, Sen. Dean Heller (R) will likely run ahead of Romney, but how close the GOP nominee can keep his numbers in the state will determine whether he returns to the Senate.
But in solid-red states like Montana and Arizona, where Romney is ahead by comfortable margins, Republican candidates Reps. Denny Rehberg (Mont.) and Jeff Flake (Ariz.) are in neck-and-neck contests.
And in solid-blue Massachusetts, which Obama is expected to win, Democrat Elizabeth Warren is leading Republican Sen. Scott Brown.
Other races have come into play in recent weeks as well.
Republicans are increasingly bullish about coal executive Tom Smith’s (R) chances against Sen. Bob Casey Jr. (D-Pa.), and Democrats showed they were worried when they began spending there this week.
While Republicans concede contests in the blue states of Maine and Connecticut, where Republican Linda McMahon has run a strong campaign, are looking less competitive than they did a few weeks ago, they believe they still have a shot at beating Sen. Sherrod Brown (D-Ohio) if Romney can carry the state. The GOP is also likely to pick up a seat in Nebraska.