Susan Davis

USA TODAY

WASHINGTON — Six states are holding primary election contests on Tuesday to set the ballots for some of 2014's most consequential general election battles.

The elections for House and Senate candidates in Arkansas, Georgia, Idaho, Kentucky, Oregon and Pennsylvania will also test the staying power of the Tea Party movement's ability to reshape the GOP.

Senate contests in Arkansas, Georgia and Kentucky are critical to determining who will control the Senate next year. Democrats currently control the chamber 55-45 – with the assistance of two independents who generally vote with them – but non-partisan election forecasters say the GOP has a shot for a takeover.

Senate Minority Leader Mitch McConnell, R-Ky., is on track to defeat primary opponent Matt Bevin, who started the primary season as an early favorite of Tea Party groups and the conservative grass roots, but he failed to translate early buzz into a competitive race. A new Bluegrass Poll by Kentucky media outlets Friday showed McConnell leading Bevin by 20 points.

McConnell's real test will come in the general election, where Democrat Alison Lundergan Grimes is polling competitively and will secure the Democratic nomination Tuesday without fuss. The same Bluegrass Poll showed a McConnell-Grimes race a dead heat.

Both campaigns will see a flood of outside money enter the race asRepublicans are lining up behind the man who will be majority leader if the GOP takes the Senate and Democrats see a rare chance to knock off a top GOP leader.

In Arkansas, Democratic Sen. Mark Pryor and Republican challenger Rep. Tom Cotton will clinch their respective nominations in a state considered one of the GOP's best chances for a pickup because of the conservative lean of the state.

In Georgia, a crowded seven-way Senate primary will be whittled to two for a July 22 runoff as no candidate is likely to earn the 50% necessary to clinch the nomination. The eventual winner will face Democrat Michelle Nunn, the daughter of former Democratic Sen. Sam Nunn, who Democrats have touted as their best 2014 recruit.

Georgia Republicans are also battling it out in a five-way primary for the nomination to take on Democratic Rep. John Barrow, a perennial election year target and one of the last of a dwindling species: white House Democrats from the Deep South.

Republicans are also watching the lower-profile Oregon GOP primary, where Monica Wehby, a surgeon, is a favorite of the party establishment – Mitt Romney endorsed her – and viewed as a potential dark horse in the race against Democratic incumbent Sen. Jeff Merkley. Republicans see political vulnerability for Oregon Democrats in large part over the state's disastrous state-run health care exchange that was scrapped after costing over $300 million.

In Idaho and Pennsylvania, the efforts of Tea Party and conservative groups to oust two veteran House Republicans will be decided. The incumbents appear poised to win reelection.

The anti-tax Club for Growth endorsed GOP candidate Bryan Smith over Rep. Mike Simpson, R-Idaho, and spent heavily in the early months of the race. But the group has throttled back its spending in the homestretch and Simpson is expected to win a ninth term.

Rep. Bill Shuster, R-Pa., has also faced Tea Party opposition in the form of primary opponent Art Halvorson, a local businessman. Halvorson's fundraising has been lackluster and Shuster is on track to secure victory. Tea Party-backed candidates have enjoyed few successes so far in 2014, but activists cheered the recent Nebraska GOP primary victory by Ben Sasse as proof that the movement is still relevant. Sasse is all but certain to win the general election in November.

Pennsylvania Democratic voters will also determine Tuesday who will take on incumbent Gov. Tom Corbett, one of the most unpopular and vulnerable GOP governors in the nation. Four Democrats are vying for the nomination, and former state revenue secretary Tom Wolf is the clear front-runner according to recent polling.