In head-to-head matchups both Democratic contenders essentially tie Republican John McCain. Hillary Clinton has a slim advantage over McCain — 46 percent to 43 percent. While McCain has a razor-thin edge over Barack Obama — 44 percent to 43 percent, according to a FOX News poll released Thursday.

Opinion Dynamics Corp. conducted the national telephone poll of 900 registered voters for FOX News from March 18 to March 19. The poll has a 3-point error margin.

The bottom line – the race is tight. These horserace numbers have shifted a bit, but essentially show little real change from February. At that time, McCain topped Clinton by 3 percentage points, and Obama had a 4 point edge over McCain.

Click here for full results. (pdf)

To further complicate things, about 1 in 7 voters (14 percent) say they would "seriously consider" voting for third-party candidate Ralph Nader. That would be enough to make Nader a factor in a tight race.

"As the November election shapes up to be another extremely close race—no matter who wins the Democratic nod—the looming "Nader factor" could once again tip the balance in key states and decide the eventual outcome," said Ernest Paicopolos, principal of Opinion Dynamics Corp.

Last month Obama led McCain among the swing voting group of independents by 11 points, but today they go for McCain by 8 points. Independents are more likely to back McCain over Clinton by 16 points today, which is similar to the 15 point advantage he had in February.

Five months ago, by almost four to one, voters believed Clinton would be the next president (9-10 October 2007). Today, 35 percent believe McCain will be the country’s next commander in chief and 26 percent believe it will be Obama. Clinton is third with 18 percent. Part of the reason for McCain’s rise on this measure could be due at least in part to the continued feuding between the Democratic contenders while he enjoys the status of the "presumptive" Republican nominee.

While majorities would be comfortable with each of the three main candidates sitting in the Oval Office, more voters say they would be at least somewhat comfortable with McCain (69 percent) as president than with Obama (62 percent) or Clinton (62 percent). McCain also has the lowest number saying they would be "not at all" comfortable with him in the White House.

By a wide 51 percent to 17 percent margin, voters say the economy is more important for the next president to focus on than homeland security. Some 30 percent say "both."

Nearly twice as many voters say they trust McCain (42 percent) to handle a national security crisis as trust Clinton (23 percent) or Obama (19 percent).

McCain (32 percent) and Clinton (30 percent) essentially tie on who would best to handle an economic crisis and Obama trails a few points behind (22 percent). As the economy becomes a bigger issue in this election, this result must be encouraging for McCain.

Furthermore, by a wide margin more voters think McCain (48 percent) would be the most dedicated to capturing Usama bin Laden, than Clinton (14 percent) or Obama (10 percent) would.

On Age, Race and Gender

There has been a lot of talk this primary season about candidate characteristics, whether it is the candidate’s age, race, gender or religion.

McCain is 71 years old. About one in four voters (23 percent) thinks his age would interfere with his ability to serve effectively as president. That is up from 13 percent in December 2006. Few Republicans (11 percent) think it would be a problem.

Is race or gender the larger obstacle to the presidency? About equal numbers say being a woman (28 percent) is a bigger challenge than being African-American (26 percent). Another 23 percent say "both" and 15 percent "neither."

Women are 5 points more slightly likely than men to say that being a woman is a bigger challenge. And more blacks (38 percent) than whites (24 percent) think being African-American makes it tougher to become president.

Being an inspirational speaker is the top reason voters think Obama is as competitive as he is in the race. Twice as many credit his speaking skills (38 percent) as say it is because he’s qualified (22 percent).

Some 14 percent say Obama has gotten where he is because he is an African-American — slightly higher than the number that thinks Clinton’s success is due to her gender (9 percent).

The main reason voters think Clinton has gotten as far as she has in the race is because of her husband Bill. By 37 percent to 28 percent, more people say she is competitive because she is the wife of a former president than because she is qualified.

The Race for the Democratic Nomination

Democrats think Obama can do a better job unifying the country (+9 points), and slightly more think he is the candidate who can beat McCain (+ 4 points).

Even so, by a slim 2 point margin Democrats say they want Clinton (40 percent) over Obama (38 percent) to be their party’s nominee. Last month, the vote preference among Democrats was split evenly at 44 percent each.

While many voters (42 percent) believe Clinton has the experience she claims, nearly half (49 percent) disagree. Among her party faithful, a 56 percent majority believes Clinton does have the experience she claims.

Overall, more voters think Obama (60 percent) would decline to be Clinton’s running mate than think she (51 percent) would turn down being Obama’s. The same holds true among Democrats, as 58 percent think Obama would say "no" to an offer to be Clinton’s vice president and 48 percent think Clinton would decline being his second.

Playing Favorites

People think the Illinois senator is the darling of the media. Nearly three times as many say Obama (43 percent) has received the most favorable press as say Clinton (16 percent) or McCain (15 percent).