Primaries have largely sorted themselves out in the most competitive Senate races in the country with Republicans — so far — avoiding the perils of 2010 and 2012 in which the party nominated a number of candidates with major electability problems in the general election. A few races can be considered truly competitive — meaning that either one or both of the national parties and the various outside groups will spend money in them. The races are tipped heavily toward Democratic-held seats. Here's a look inside some of the key Senate campaigns:

Colorado (Democratic-controlled): While most people look at the North Carolina race as the one on which Senate control might swing, this race between Democratic Sen. Mark Udall and Republican Rep. Cory Gardner could easily fit that bill too. Polling done by Quinnipiac University in late April showed the race a dead heat and both sides acknowledge the race is and will stay close. Udall is on TV now bashing Gardner as too conservative — particularly on abortion — and Democrats think Gardner's record is full of bad votes.

Alaska (Democratic-controlled): Conservative blogger Erick Erickson this week endorsed Lt. Gov. Mead Treadwell, R, giving the long-struggling candidate a much-needed boost. But it's not going to change the fact that former Attorney General Dan Sullivan is the clear front-runner for the Republican nomination. Sullivan has both establishment and Tea Party money in his corner and is well on his way to a fall showdown against Democratic Sen. Mark Begich.

Kentucky (Republican-controlled): Republicans are feeling more confident about Sen. Mitch McConnell's chances following his convincing primary victory in May, and their sense that the GOP is quickly uniting behind him. President Obama didn't do Democrat Alison Lundergan Grimes any favors with his announcement on power plants earlier this month. But McConnell's numbers suggest his vote ceiling is very low. And, in a cycle where they have very few opportunities, Democrats will pour everything they have into this one.

Arkansas (Democratic-controlled): Republican Rep. Tom Cotton's campaign released an internal poll claiming a lead over Sen. Mark Pryor, D. The release was meant to counteract a growing narrative that Pryor is not nearly as vulnerable as he once seemed. But the most notable part of the survey was in the trend line: Cotton was polling the race in February in 2013, when he was still a brand-new member of the House. The revelation probably won't help Cotton in his chief task right now: Humanizing himself and showing voters that he's not just a super-ambitious pol championed by national conservative groups.

North Carolina (Democratic-controlled): Democrats tried to make an issue of Republican state House Speaker Thom Tillis referring to white people as the "traditional population" of North Carolina. We wouldn't call that a campaign-stopping gaffe, but given Democrats would love to motivate minority voters in a midterm election, Tillis should probably choose his words a little more carefully. The race between Tillis and Democratic Sen. Kay Hagan remains very close.

Louisiana (Democratic-controlled): Expect Democratic Sen. Mary Landrieu to emphasize her role as head of the Senate Energy Committee for the rest of the campaign. She passed a bill out of her committee this week that would bypass President Obama and approve the Keystone XL pipeline. The question is whether the emphasis on energy will be enough to overcome a capable Republican opponent in Rep. Bill Cassidy in a state where the president is deeply unpopular. Those are big obstacles.

Montana (Democratic-controlled): Both appointed Democratic Sen. John Walsh and Republican Rep. Steve Daines easily dispatched nominal primary challenges on June 3 and formally began a race that both campaigns had already been waging for months. There's very little public polling in the race, but the consensus is that Daines starts the general election with an edge — and is likely to benefit from a national political environment benefiting Republicans.

West Virginia (Democratic-controlled): Republican Rep. Shelley Moore Capito likely wrapped up this Senate seat in November 2012 when she announced her candidacy even though Democratic Sen. Jay Rockefeller had yet to announce his retirement. Democrats convinced Secretary of State Natalie Tennant to run but she started the race at a disadvantage because of Capito's early start and the dislike of the national Democratic Party in the state. A recent nonpartisan poll put Capito up, 49 percent to 38 percent.

South Dakota (Democratic-controlled): This seat seems most likely to flip. Former Republican Gov. Mike Rounds remains a strong favorite against Democrat Rick Weiland, but this race also includes former three-term GOP U.S. Sen. Larry Pressler and former GOP state Sen. Gordon Howie running as independents. Neither has raised significant amounts of money, but maybe Pressler can steal enough of Rounds' votes that this race becomes competitive. Weiland can hope.