"Any gaffes will be magnified by the monstrous media contingent he's got in tow," Michael Saul writes in the New York Daily News.
"One goal of the trip is to quell doubts about whether the 46-year-old, first-term senator has the background and skills to handle national security concerns in a post-9/11 world of shifting alliances and terrorist threats," USA Today's Kathy Kiely writes. "The risk is that a misstep could enhance those doubts or an overstep create a backlash."
Then comes Europe, where different kinds of risks loom: "In a presidential campaign where the Democrat faces an especially intense variation of a familiar Republican assault -- that he is, in some sense, not 'one of us,' the trip abroad represents an opportunity for Obama to assert that he is, rather, not one of them," Politico's Ben Smith writes. "His popularity in Europe, unmatched among American politicians, could hurt him politically, however, if rapturous foreign crowds are seen as emblematic of his purported foreignness."
"If Britain and Europe could vote, he would win the White House in a landslide," Sarah Baxter writes in the Times of London. "In America, however, Obama is struggling to convince voters that he is The Chosen One. While he is supported abroad by almost everybody from French communists to German greens and plenty of British conservatives, his victory at home is far from assured."
The big event: It could be a crowd of a million-plus in Berlin Thursday, for what the campaign is calling a "major speech on the historic U.S.-German partnership, and the need to strengthen transatlantic relations to meet 21st century challenges."
Will he do anything that isn't scripted in advance? And if he doesn't, how long before that becomes the story?
"There won't be many opportunities for gaffes," Noam Scheiber writes for The New Republic. "Gaffes generally require a modicum of spontaneity. And the Obama expedition, far more so than the typical campaign appearance, is being stage managed to the extreme."
"We'll see if the pattern changes, but if he keeps this up all week he'll have done exactly what he does at home: cling to that teleprompter and operate only within his 'comfort zone,'" Jennifer Rubin blogs for Commentary. "Does he lack the confidence and ability to operate without a net?"
As for McCain's day -- he raises money alongside former President George H.W. Bush in Kennebunkport, Maine, on Monday. (Is this really the day he needs a boost from a Bush?)
He also attends an outdoor event at the Maine Military Museum in South Portland, "searching for votes and money in a state that went Democratic in the last four national elections, yet has a soft spot for mavericks and GOP moderates," per Dieter Bradbury of Blethen Maine Newspapers.
Meanwhile, Obama and McCain are set to share their first stage of the general election campaign: "The Rev. Rick Warren has persuaded the candidates to attend a forum at his Saddleback Church, in Lake Forest, Calif., on Aug. 16," The New York Times' Jim Rutenberg reports.
"In an interview, Mr. Warren said over the weekend that the presidential candidates would appear together for a moment but that he would interview them in succession at his megachurch," Rutenberg writes. "He said that both had readily agreed, perhaps reflecting how each candidate is courting the evangelical audience to whom Mr. Warren ministers."