The Centers for Disease Control and Prevention has announced a new set of protocols for travelers arriving from countries affected by Ebola. Travelers will be required to provide the agency with contact information for themselves and a relative or friend when they arrive, and to report their body temperature and any possible symptoms twice a day to a local hospital for the next 21 days.

Several dozen lawmakers had called for a ban on travelers arriving from Sierra Leone, Liberia and Guinea, and House Speaker John Boehner has said the president should consider the idea. The real danger, argues Bret Stephens, is a widespread panic, which a travel ban would prevent. As Jonathan Cohn writes, however, most public health experts doubt that a ban would be a good idea.

"I’m not at all convinced that shutting down air travel from the west coast of Africa to America is going to be effective," said Roy Anderson, a leading British epidemiologist.

Most people who are infected with Ebola develop symptoms within about 11 days, which means that it would be easy for a traveler to leave Liberia for Europe, spend a few days there, and then bring the virus to the United States.

What's more, even supporters of a ban acknowledge exceptions should be made for essential travel for military and medical personnel. As the disease spreads, the chances that it returns to the United States increase. A ban can only delay the next case, and not for very long.

At the request of Wonkbook, a group of researchers based at Northeastern University led by Alessandro Vespignani modeled the effects of reducing air traffic by 95 percent between the three countries and the rest of the world. (Traffic has already declined by about 80 percent, they estimate.) The result was that the next case would arrive in the United States about a month later -- on average, sometime in the middle of December instead of the middle of next month.

Forecasting the spread of Ebola requires making assumptions about how rapidly the virus is spreading in West Africa and whether other countries will be able to control outbreaks, and Anderson warned against putting too much credence in any one of the several models that have been published. (According to another forecast, published this week in Lancet, about three passengers with the virus will fly to another country every month.)

Still, many experts say a ban could be short-sighted, as Nick Kristof writes. Stopping all flights might make it more difficult for medical personnel to get to the affected countries, where the CDC has predicted that hundreds of thousands could be dead by January, and help to control the epidemic at its source.

Georgetown University's Lawrence Gostin said the new policies were a reasonable response to the pressure on the White House from lawmakers. "If it’s a political compromise that avoids truly catastrophic decision like a travel ban, I think it will be well worth it," he said. Still, Gostin said, it's unclear who will enforce the new monitoring protocol, and whether local authorities will have the resources to keep track of the 150 travelers or so who arrive daily from West Africa.

"You protect America, you protect western Europe best, by controlling the epidemic in these three worst affected countries," Anderson said. If protecting the homeland is the goal, there is still work to be done.

What's in Wonkbook: 1) Canadian Parliament attacked 2) Opinions: Obamacare, G.O.P. governors, IBM and the female vote 3) Leaks in the Ferguson, Mo. investigation 4) Blackwater guards convicted in Nisour Square massacre 5) Defective airbags, Arkansas demographics and more.

Number of the day: 1.7 percent. That's the rate at which prices have risen over the past 12 months, according to the monthly report from the Bureau of Labor Statistics. The Federal Reserve's target of 2 percent is nowhere in sight. Lucia Mutikani for Reuters.

Chart of the day:

The United States spent $7.6 billion trying to end opium production in Afghanistan. You see what that money bought here. Chris Ingraham in The Washington Post.

1. Top story: Ottawa is locked down after a fatal shooting

Prime Minister Stephen Harper calls the incident a "terrorist" act. A soldier is dead as well as the suspect, Michael Zehaf-Bibeau, a Canadian known to authorities who had recently seized his passport. Josh Wingrove, Steven Chase, Bill Curry and Jill Mahoney in The Globe and Mail.

A Canadian convert to violent Islam ran down and killed a soldier with his car on Monday. Martin Couture-Rouleau, a young father and the owner of a small business, wanted to become a jihadi. Like  Zehaf-Bibeau, he had had his passport seized. Police fatally shot him after a chase. Ingrid Peritz, Tu Thanh Ha and Les Perreaux in The Globe and Mail.

Authorities had taken his passport, but they didn't have evidence of a crime. Couture-Rouleau was not "a candidate for a viable prosecution" and was let go, though police were trying to monitor him. Colin Freeze in The Globe and Mail

In the United States, merely attempting to join a terrorist group is a crime. The Federal Bureau of Investigation arrested and charged Mohammed Hamzah Khan at O'Hare International Airport earlier this month, saying he planned to travel to Syria to fight for the Islamic State. Andrew Grossman in The Wall Street Journal.

Terrorists returning from abroad aren't a major threat in the United States. "We're going to know who these guys are, and we're going to watch them closely as they transit home," one expert said. Zack Beauchamp in Vox.

More Canadians are traveling to fight overseas. At least 30 Canadians are fighting for organizations identified as terrorist in Syria, according to a government report. Marc Santora in The New York Times.

2. Top opinions: Obamacare, Republican governors, IBM and female voters

PONNURU: Obamacare can't be fixed. A Senate bill adding a high-deductible, low-premium "copper" plan wouldn't address the basic problems with the law.  Bloomberg.

CASSIDY: Right-wing Republican governors are in trouble. Kansas Gov. Sam Brownback, Wisconsin Gov. Scott Walker, and Florida Gov. Rick Scott are fighting for survival after implementing the agenda of the extreme right. The New Yorker.

MEYERSON: The implosion of IBM is the story of the U.S. corporate sector. Instead of investing in new technologies and talented people, the company gave financial gifts to its investors -- until that strategy backfired this week. American companies have been systematically making the same mistake. The Washington Post.

COLLINS: When it comes to female voters in the midterm election, candidates are trying too hard. Women aren't fooled by their awkward, blatant pandering. The New York Times.

3. Leaks in the Ferguson case support the officer's story

Witness testimony and physical evidence support Officer Darren Wilson's account of the shooting, sources say. According to people familiar with the investigation, the evidence suggests Wilson and Michael Brown struggled inside the car, and that Brown was moving toward the officer when he shot and killed the young man. Kimberly Kindy and Sari Horwitz in The Washington Post.

Wilson claims Brown shoved him back inside his car when he tried to step out of it. The two began to struggle, and Wilson drew his weapon, the officer testified. This account, published last week, "did not come Ferguson Police Department or from officials whose activities are being investigated as part of the civil rights inquiry." Michael Schmidt, Matt Apuzzo and Julie Bosman in The New York Times.

The St. Louis County autopsy showed Brown received a gunshot wound to his hand at close range. The conclusion, suggesting a struggle for the weapon, is based on an analysis by experts not directly involved in the case. Christine Byers and Blythe Bernhard in the St. Louis Post-Dispatch.

The Department of Justice condemns the leaks. In a statement, a spokeswoman calls the leaks "irresponsible and highly troubling," saying they were selective and appear to be an attempt to influence public opinion. Matt Pearce in the Los Angeles Times

Arbitrary policing continued for weeks in response to protests. For example, Ferguson police arrested people and released them without paperwork, or told protesters those arrested would be released if the crowd dispersed.  Kimberly Kindy and Wesley Lowery in The Washington Post.

4. Four Blackwater guards are convicted

One was convicted of murder and three of manslaughter in a massacre in Baghdad's Nisour Square. The conviction took seven years and was hampered by missteps by the government. Matt Apuzzo in The New York Times.

Legislation that would clarify how such cases should be prosecuted has stalled. "It should not have taken this long for justice to be served," said Sen. Patrick Leahy (D-Vt.), the author of the bill. Spencer Hsu, Victoria St. Martin and Keith L. Alexander in The Washington Post.

LINDA ROBINSON: Contractors are never going away. In 2011, contractors -- once rare on the battlefield -- constituted 50 percent of the total force in Afghanistan and Iraq. Their industry could become more transparent and accountable, but it can't be eliminated: "Paying for a soldier’s lifetime health care and retirement pension is far more costly than hiring contractors, even at fairly exorbitant rates." (Review of "The Invisible Soldiers" by Ann Hagerdorn. The Wall Street Journal.

5. In case you missed it

Economists pan House Republicans' agenda. Tax and immigration reform are more important than approving the Keystone XL pipeline. Jackie Calmes in The New York Times.

Lawmakers call for a national recall of defective airbags. Already, 11.6 million vehicles have been recalled in the United States. Hiroko Tabuchi and Aaron Kessler in The New York Times.

Three times as many vehicles have been recalled this year as were sold in 2013. Yet drivers are getting contradictory messages, and authorities don't agree about which vehicles are dangerous. "The disjointed recall system patched together by automakers and regulators is leaving millions of broken vehicles still on the road." Drew Harwell in The Washington Post.

In Arkansas, demographic trends favor Republicans, not Democrats. That's because there are fewer older, conservative white Democrats every year, and the population in the state's reliably Republican exurbs is growing quickly. Nate Cohn in The New York Times.

The National Weather Service has stopped getting data from some satellites. Forecasts shouldn't be affected, a spokesman said, but the service has been hampered by inadequate funding and obsolete technology. Jason Samenow in The Washington Post.