At least 14 Republican members of Congress have refused to endorse or publicly support Sen. John McCain for president, and more than a dozen others declined to answer whether they back the Arizona senator.

Many of the recalcitrant GOP members declined to detail their reasons for withholding support, but Rep. John Peterson (R-Pa.) expressed major concerns about McCain’s energy policies and Rep. Walter Jones (R-N.C.) cited the Iraq war.

In recent weeks, much of the discussion and debate about party unity has been on the Democrats’ side, amid their protracted presidential primary. Yet achieving harmony is a concern on both sides of the aisle this year.

It is not unusual for certain factions of the Democratic and Republican parties not to embrace their respective candidates for president. McCain’s campaign seized on some Democrats’ reticence about Sen. Barack Obama (D-Ill.), issuing a release on Tuesday that highlighted that Rep. Dan Boren (D-Okla.) is not endorsing the presumptive nominee. While some conservative Democrats have yet to endorse Obama and didn’t back Sen. John Kerry (D-Mass.) in 2004, there are both centrist and conservative Republicans representing various parts of the country who are not embracing McCain.

Republican members who have not endorsed or publicly backed McCain include Sens. Chuck Hagel (Neb.) and Jeff Sessions (Ala.) and Reps. Jones, Peterson, John Doolittle (Calif.), Randy Forbes (Va.), Wayne Gilchrest (Md.), Virgil Goode (Va.), Tim Murphy (Pa.), Ron Paul (Texas), Ted Poe (Texas), Todd Tiahrt (Kan.), Dave Weldon (Fla.) and Frank Wolf (Va.). [Wolf contacted The Hill following publication of the article to correct his staff’s error. His staff had said he has “yet to endorse McCain” and did not return follow-up phone calls this week].

Throughout his career in the House and Senate, McCain has been at odds with his party on a range of issues, including campaign finance reform, earmarks, immigration, healthcare, taxes and energy.

Some Senate Republicans were especially irked with McCain’s role in the “Gang of 14” deal on judicial nominations.

Rep. Tom Tancredo (R-Colo.), who has been sharply critical of McCain on immigration, told The Hill in February, “I don’t like McCain. I don’t like him at all.”

Tancredo spokesman Mac Zimmerman said Tancredo won’t endorse McCain because he fears the senator would repudiate it like he did with the formal backing of controversial pastor John Hagee.

However, Tancredo told ABC News this week he will reluctantly vote for McCain.

Gilchrest and Hagel, who disagree with McCain’s views on Iraq, have been mum on their endorsements. Kathy Hicks, spokeswoman for Gilchrest, said, “Since he was not reelected to public office, he’s keeping his thoughts private.” Gilchrest lost in a Republican primary earlier this year.

Jones, who has voted repeatedly with Democrats on Iraq, said he can’t back McCain until he gets “a better explanation of the plans for Iraq and more discussion on the economy.” Jones added that no one from McCain’s campaign has reached out to him.