ANNAPOLIS, Maryland (CNN) -- Narrowing down 20 or so names on a list of potential Republican vice presidential candidates will take weeks, if not months, Sen. John McCain told reporters Wednesday.
Sen. John McCain brings his biographical tour to the U.S. Naval Academy in Annapolis, Maryland, on Wednesday.
"It's the same process that has been used by Democrats and Republicans," the presumptive GOP presidential nominee said on his campaign bus.
"It's not an unusual thing. You put the list together, and then you just could do a cursory kind of a look that I guess you could do on Google."
McCain did not discuss who is on the list. See who McCain may be considering »
The Arizona Republican said he would like to have his running mate picked by the national convention in September.
"I'd love to do it earlier in the run than later, but it depends on the process," he said. "We just really haven't gotten far enough along in the whole thing to really be able to even predict what we're doing, seriously." Watch McCain on the selection process »
McCain said he wanted to avoid mistakes that other presidential nominees have made when picking a running mate in a rushed process.
McCain pointed to what happened in 1988 with Dan Quayle, saying the former vice president "had not been briefed and prepared for some of the questions."
"I'm a great friend of Dan Quayle's, and I think he was a fine senator . . . . I just think you have to have a measured process, [and] make sure that you have taken . . . all the factors into consideration and then decide," he said.
McCain on Wednesday also rejected an assessment by a prominent Christian conservative leader that he has failed to unite the Republican Party. Watch McCain call the party 'largely unified' »
In a statement in Wednesday's The Wall Street Journal, James Dobson, founder of Focus on the Family, wrote he had seen no evidence that McCain "is successfully unifying the Republican Party or drawing conservatives into his fold."
"To the contrary, he seems intent on driving them away," Dobson added.
In an interview with CNN, McCain said he respected Dobson's views but disagreed, citing the endorsements of his former rivals and polling data to show that the party is rallying behind him.
"I'm very pleased at the polling data that shows that our party is very unified," McCain said. "More Republicans say they'll vote for me than Democrats say that they will vote for either Sen. Obama or Sen. Clinton.
"My job now is to try to energize our party so that we get the kind of energy associated with this campaign, which I think we can do in the coming months."
McCain said he has never spoken with Dobson but would be willing to do so.
In his statement, Dobson said McCain had not reached out to "pro-family leaders" or changed his views on positions that "trouble" social conservatives, pointing to the candidate's support for embryonic stem cell research and stance to allow states to set their own definitions of marriage.
The latter is an apparent reference to McCain's opposition to a constitutional amendment defining marriage as between a man and woman.
McCain does believe marriage should be defined as being between a man and woman, his campaign told CNN, but the candidate objected to the Federal Marriage Amendment because he thinks it's a matter for the states to resolve.
In his statement to The Wall Street Journal, Dobson also faulted the senator for his foreign policy speech last week in which he called for more collaboration with allies, closure of the military prison at Guantanamo Bay, Cuba, and a new global warming treaty.
"These policies frustrated conservatives, whom McCain seems to have written off," Dobson wrote.
Dobson's statement to the paper comes as McCain continues his "Service to America " tour, a series of stops to locations that played a significant role in his life. Watch analysts debate whether McCain should go on tour »
On Wednesday, McCain spoke at the U.S. Naval Academy in Annapolis, Maryland, where he graduated in 1958, following in the footsteps of his father and grandfather.
Later Wednesday, he traveled to Pensacola, Florida, where he trained to be a fighter pilot. McCain went on to fight in the Vietnam War and was held as a prisoner of war after his plane was shot down.
McCain joked about his "misspent youth" and said a "nagging conscience" required an "honest appraisal of my record and character" at the Naval Academy.
"In truth, my four years at the Naval Academy were not notable for exemplary virtue or academic achievement but rather for the impressive catalog of demerits I managed to accumulate," McCain said.
"By my reckoning, at the end of my second class year, I had marched enough extra duty to take me to Baltimore and back 17 times -- which, if not a record, certainly ranks somewhere very near the top."
But McCain said he learned the lessons of discipline that served him later in life while at Annapolis.
"When I left the academy, I was not even aware I had learned that lesson. In a later crisis, I would suffer a genuine attack on my dignity, an attack, unlike the affronts I had exaggerated as a boy, that left me desperate and uncertain," McCain said in an apparent reference to his time as a POW. Watch as McCain praises public service »
"It was then I would recall, awakened by the example of men who shared my circumstances, the lesson that the academy in its venerable and enduring way had labored to impress upon me. It changed my life forever. I had found my cause: citizenship in the greatest nation on Earth," he said. Watch McCain talk about the greatest lesson he learned » E-mail to a friend
CNN's Dana Bash contributed to this report.