President Obama is building a billion-dollar campaign with the massive advantages of incumbency behind him, and the most notable thing going on in the field of potential Republican challengers is the discussion by a reality-show host about Obama’s birth certificate.

Not exactly where Republicans would like to be 20 months before an election that both sides agree will be a defining political moment for a generation.

If Obama wins, it will be a mandate for his policies and the nexus of a new Democratic coalition. If Obama loses, it will mean the reversal of his laws and the validation of the Republican move toward blue-collar populism.

But whether Donald Trump believes Obama was born in Honolulu or Kenya or the planet Krypton isn’t of much practical concern for Republicans. Trump has flirted twice before with seeking the presidency. He may be running for office or he may be running an ingenious publicity campaign for the next season of “The Apprentice.”

But it says something about the sclerotic nature of the Republican field that Trump and his speculation about Obama’s birthplace has generated so much attention. The fact is, that there just isn’t much else to talk about.

Only one top-tier candidate, former Minnesota Gov. Tim Pawlenty, has formed an exploratory committee. The rest, particularly former Massachusetts Gov. Mitt Romney, are still operating in the shadow world of pre-pre candidacy – as former House Speaker Newt Gingrich described it, being “excited about exploring.”

By this point in 2007, the Republican field had mostly taken shape. All of the major contenders, save slowpoke Fred Thompson, had already formed committees so they could start raising money and solidifying their staffs.

John McCain, Mitt Romney, Rudy Giuliani and Mike Huckabee were all already on paper with the Federal Election Commission.

Once change from 2008 is that candidates like Romney and Gingrich are able to use their political action committees as campaigns in waiting. They can staff up, pay for travel and maintain a national organization without having to take the dive into actual candidacy.

But why not? Almost running sounds like almost leadership; tentative and legalistic at a time when Republican primary voters are looking for inspiration.

Smart Democrats, notably FOX News colleague Juan Williams, have maintained that the Republicans are afraid of Obama and that they know in their guts that they can’t unseat the commander in chief. Certainly some in the Republican Party are gripped with the same doubts that kept Democrats sitting on the sidelines in 1992.

Back then, big-name Democrats like New York Gov. Mario Cuomo and Tennessee Sen. Al Gore were happy to let an Arkie governor with some bimbo baggage try to knock off the sitting president who had just led the first victorious land war waged by the United States since World War II.

But Obama looks eminently beatable. It will be hard to do, given all of the president’s considerable advantages – Air Force One, the big blue podium, the gobs and gobs of money from corporate patrons, the puffball coverage from the establishment press, etc. – but Obama has engendered little love and much skepticism in 798 days in office.

The potential contenders wouldn’t have come this far if they didn’t think they could beat Obama. What is more likely holding them back is the fear of a demolition derby in the Republican primaries.

Potential candidates with financial means and little to lose – folks like Rep. Michelle Bachmann, R-Minn., or pizza mogul Herman Cain – scare the top-tier contenders. In an era of political decentralization via the Internet and at a time when insiderdom is considered a taint by many Republican activists, there is great concern that lots of money and a sound strategy will not be sufficient anymore.

Candidates other than happy warrior Pawlenty have stayed out of the pool on the belief that it will be a long, punishing primary season and that there will be little to gain by starting it any sooner than necessary.

But Obama has already started limbering up his fundraising leviathan and is expected to announce his candidate filing sometime in the next few weeks. As the Republicans try to wait each other out, Obama builds his beast.

Republicans today may be worried about getting banged up in the primaries, but the longer view suggests that beating an incumbent president is certainly a 20-month job. If Republicans waste too much time in their current game of chicken, they only increase Obama’s advantage.

Chris Stirewalt is FOX News’ digital politics editor. His political note, Power Play, is available every weekday morning at FOXNEWS.COM.

Chris Stirewalt joined Fox News Channel (FNC) in July of 2010 and serves as digital politics editor based in Washington, D.C.  Additionally, he authors the daily "Fox News First" political news note and hosts "Power Play," a feature video series, on FoxNews.com. Stirewalt makes frequent appearances on the network, including "The Kelly File," "Special Report with Bret Baier," and "Fox News Sunday with Chris Wallace."  He also provides expert political analysis for Fox News coverage of state, congressional and presidential elections.