LAS VEGAS - Freshman U.S. Rep. Joe Heck has been running for re-election since he won in November, trying to fend off unrelenting attacks on his five-month-old voting record as the Democratic Party has saturated his Las Vegas district with billboards, phone calls and mailers.

But the Republican lawmaker has no opponent. His would-be rivals, it seems, are waiting for the Legislature to complete the once-every-decade process of redrawing political boundaries before they decide whether to challenge him in 2012.

Similar phantom campaigns are unfolding in other states where district lines and potential candidates have been slow to emerge. States are in the midst of drawing new political maps for congressional and legislative districts based on the 2010 census. The uncertainty surrounding the final lines is delaying candidates from jumping in to races on the ballot in November 2012.

"I have basically tried to keep whatever options I have open," says Danny Tarkanian, a tea party supporter who lost the GOP Senate nomination in Nevada last year but is expected to run for Congress.

Some incumbents will find their districts redrawn to help a rival party leader. A few challengers will learn they now live outside the district of the U.S. representative they had hoped to unseat. In the best scenario, candidates will gain an advantage in a district that already favored them.

Current districts will change or even vanish, based on population totals and the influences of the political party in power in each state. In most states, state legislators will redraw the maps, with the governor holding veto power.

Recent ballot initiatives requiring partisan-free redistricting in Florida and California are contributing to the unpredictability surrounding the upcoming campaigns and could further stall candidates if the boundaries end up in court.

Many U.S. House members could be in trouble.

In Indiana, Democratic Rep. Joe Donnelly has decided to run for the U.S. Senate to flee his increasingly Republican district. GOP incumbents in upstate New York face unemployment as the state prepares to eliminate two House seats to reflect the area's shrinking population.

Even in the seven states with just one House member, redrawn legislative districts could foster unwanted competition as pushed out state senators and representatives seek higher office.

Only a few states had passed redistricting maps as of early May. Most states will tackle the boundaries later this year or early next year.

The U.S. Department of Justice must approve the plans of 16 states with a history of election violations, including Texas and Florida. All plans must be in place by the time candidates are required to file documents indicating they will run in 2012.

"Almost every state will be done by early spring of next year," said Tim Storey, a redistricting expert for the National Conference of State Legislatures. "It really varies from state to state and there are a lot of political considerations."

Democratic and Republican organizations tasked with electing their party members to the U.S. House are homing in on candidates with a whiff of vulnerability.

In Utah, Republicans are going after Rep. Jim Matheson, the state's lone Democrat in the U.S. House. The National Republican Congressional Committee released a 30-second television spot in February highlighting Matheson's 2009 vote to pass the $787 billion stimulus bill. But a Republican has not announced a campaign against Matheson, now in his sixth term.

Matheson is waiting for the state to pass its new congressional boundaries before he decides whether to run for re-election. If the odds are against him, he said he might campaign for governor or the U.S. Senate.

"I am running for something," he said. "I am not sure what."

In Florida, voters recently passed a ballot initiative requiring that districts be continuously connected. Democrats are hoping to unseat as many of the GOP's 19 House members as possible, but few challengers have announced they will run. The state isn't expected to finish its redistricting process until mid-2012, a timeline that favors incumbents because they can spend months raising money and campaigning without the distraction of a rival.

"If you don't have a district drawn, it's hard for people to analyze it, it's hard for people to say whether you have a shot," said Eric Jotkoff, spokesman for the Florida Democratic Party.

There are a few exceptions.

Expecting that the district just north of Miami held by Republican Rep. Allen West will become more Democratic, former West Palm Beach Mayor Lois Frankel is attempting to oust the freshman tea party favorite.

In California, Democratic Assemblyman Anthony Portantino has begun raising money to take on GOP U.S. Rep. David Dreier. For the first time, a 14-member citizens panel with representatives from all parties will design California's congressional boundaries.

"The district will be established a year before the election," Portantino estimated. "Obviously, the goal is to be prepared."