(CBS News) With less than 100 days to go until the November elections, all eyes are on Mitt Romney and President Obama as they battle it out for the presidency in a tight and increasingly contentious race. But a handful of competitive Senate races across the country could also have significant bearing on the nation's political future - and not just because control of the Senate is up for grabs. Here are four things to watch out for this fall:
A Tea Party resurgence?
For all its grassroots rabble-rousing in 2010, the Tea Party, in the 2012 election cycle, seemed to be losing some steam. Unable - or unwilling - to unify behind a single presidential candidate in the Republican nominating process, skeptics questioned the group's ability to have a meaningful impact this time around.
On the heels of a handful of recent Senate primary victories, Tea Party leaders are combating that assertion.
On Tuesday,, a Tea Party-backed Republican with no history in elected office, as the state's GOP Senate nominee. Besting David Dewhurst, the state's lieutenant governor and a longtime figure of the Texas Republican establishment, the race was one of a few GOP primary contests this year in which an established politician with party support was defeated by a more staunchly conservative political newcomer.
The Tea Party gains this year have been relatively modest: In the Indiana Republican primary, the famously moderate GOP Senator Richard Lugar was ousted by the Tea Party-backed Richard Mourdock; Tea Party forces worked on behalf of Wisconsin Governor Scott Walker in his successful effort to defeat a recall challenge; and in Nebraska's GOP primary, relative unknown Deb Fischer beat not only Attorney General Jon Bruning, but also the race's Tea Party-backed candidate. Her victory, however, was largely attributed to the massive amount of money that her two opponents - and their backers - put into tearing each other down.
Still, the evidence would suggest that Tea Party-oriented groups and politicians are developing new methodology for getting their candidates elected. And with a handful of victories under their belts, Tea Party proponents may well be able to convince others to join in.
"The false narrative continues to be written that the tea party is dead, and 2012 will not be like 2010," said Tea Party Express Chairman Amy Kremer in a Tuesday night statement. "Tonight we sent a message that should shake Obama's Chicago headquarters: Texas not only is going to be staying a red state, but the tea party is alive and ready to own 2012."
Outside groups: Spending early and often
Throughout the country, outside groups have had an enormous influence on how the 2012 election has played out. But Senate races in a handful of states, where conservative outside groups spent inordinate amounts of money to support candidates who shared their values, may be weathervanes for how outside groups influence Senate races going forward.
"They get the most bang for the buck in the primary," said Larry Sabato, director of the University of Virginia's Center for Politics, of how a super PAC can influence a non-national race.
It's a lesson that the Club for Growth, a super PAC that advocates a conservative vision of limited government and often supports Tea Party candidates, seems to grasp well. After helping to lead Richard Mourdock to victory in Indiana, the group threw $5.5 million behind Ted Cruz's efforts in Texas. As in Indiana, the establishment candidate's defeat was seen not just as a boon for the Tea Party, but also as proof that outside groups, particularly in the primary process, can tangibly influence what their party looks like in Congress.
"Club for Growth Action has played an important factor in the Texas Senate race on behalf of Ted Cruz," read a memo released Monday by group. "After playing a similar role in the defeat of Senator Richard Lugar (R-IN), Club for Growth Action is set to play a major role in the composition of the United States Senate next year."
It's not the only group thinking that way.
According to Sabato, any super PACs that haven't already gotten the memo in the 2012 election cycle are sure to catch on in 2014's Senate primaries.
"They'll start earlier and have an impact there," he said. "I suspect that some of the super PACs will also move into voter mobilization -- which in a midterm election would make an enormous difference."
The presidential trickle-down effect
Outside contributions are expected to impact races across the country, but the national political establishment will also play a determining role in Senate races nationwide.
As President Obama and Mitt Romney ramp up their campaign efforts across the nation, their campaigns, along with the national party apparatus, will flood key battleground states with money, volunteers, and the organization needed to build strong grassroots organizations aimed at mobilizing and registering voters. In states like Virginia, where the Senate race between Democrat Tim Kaine and Republican George Allen is expected to be almost as close as the presidential contest, that could make a huge difference for both candidates.
But there's a flip side to that coin: Not all Senate contenders want to be associated with the presidential candidate on the top of their ticket, particularly if that candidate ends up losing.
"The coattail effect is the defining factor in most of the key Senate races," said Sabato. "I would strongly suspect that in the close races a large majority of voters will end up falling into the party column of the winning presidential candidate in that state."
In Massachusetts, which Mr. Obama is expected to win handily, he'll likely help out the prospects of Elizabeth Warren, who is battling incumbent Republican Scott Brown for his seat. But in Missouri, for instance, or Montana, where Romney has an edge, he's likely to hurt incumbent Democratic senators like Claire McCaskill and Jon Tester.
"The disadvantage is in distinguishing yourself from your ticket-mate," says Sabato. "Frankly, it's almost impossible."
The wildcard possibility
These days, thanks to endless partisan rancor and its resulting gridlock, Congress is infamous for a perceived inability to get things done. Democrats and Republicans vote almost uniformly along party lines, and a number of Congress' more moderate members have either been voted out of office or decided not to run for it.
As a result, those senators who do occasionally buck party trends wield significant influence in the chamber. Scott Brown, who is in the midst of waging a tooth-and-nail re-election battle against Elizabeth Warren in Massachusetts, has touted his cooperation with Democratic senators, as well as President Obama, as evidence that he puts progress over politics.
Meanwhile, in Maine, the independent former governor Angus King is running to replace outgoing Sen. Olympia Snowe - herself a longtime moderate Republican who cited partisan acrimony as part of her reason for her decision not to seek re-election. King has vowed that, if elected, he would take "the best ideas, regardless of party, to find common sense solutions" in the Senate.
"Building bipartisan legislation would be a priority," said campaign spokesperson Crystal Canney, in an email. Canney cited Snowe's apparent frustration with the current state of Congress as a prime source of King's desire to serve.
"Angus King is running for U.S. Senate for exactly the reasons Olympia Snowe has stated she is leaving. He has said often, if a woman of Snowe's character, skill and intellect is saying the system isn't working then it's time for a new approach," Canney said. "King would again not be beholden to party and would work with both sides of the aisle and look for opportunities to build a coalition of like minded people in the Senate. His track record shows it's possible."
King is largely expected to vote with Democrats if elected, as Brown is expected to vote with Republicans. But if, as is anticipated, one party holds a razor-thin majority in the Senate, both could be key swing votes in the 112th Congress.