Presidential nominees Sens. John McCain (R- Ariz.) and Barack Obama (D-Ill.) engaged in a sharp debate this evening, demonstrating clear differences in viewpoints and approach on a wide range of domestic and foreign policy issues.

Putting aside any concern that he will be tagged as too old, McCain repeatedly emphasized his long years of experience, seeking to contrast his deep involvement in affairs of state with Obama’s comparatively thin Washington résumé. Obama sought to move the debate to issues where he believes he has an advantage, like taxes, regulation and the decision by President Bush to launch the Iraq War.

McCain and Obama attacked aggressively throughout the debate, though Obama more frequently sought to defend himself against and dissect his opponent’s charges – rather than adopting the time-honored debate tactic of ignoring attacks and offering affirmative views. Obama repeatedly began his statements with phrases like “Let’s talk about this,” or “hold on” of “I’ve got to correct the record.”

Obama took perhaps his best shots early in the debate, when the discussion focused on the economy and particularly the $700 billion financial system bailout plan proposed by Bush and being hashed out now on Capitol Hill. Obama hammered home the theme that Republicans like Bush and McCain generally oppose regulation, blaming such a stance for the meltdown on Wall Street. Obama emphasized his support for middle-class tax cuts and sought to contrast it with what he said was McCain’s backing for giveaways to the rich and to oil companies.

McCain highlighted his own record opposing earmark spending – and noting Obama’s earmark requests – repeatedly returned to the issue and linked it to greed and corruption. He also spoke of his support for nuclear power and drilling, hot-button issues where Republicans believe they have an advantage.

In what appeared to be a new proposal, McCain said he wants a spending freeze on all but national security and veterans-related spending, as well as in other select areas. Obama responded that such an approach would be “using a hatchet when we need a scalpel.”

Obama advocated traditional Democratic positions like increasing investments in education and alternative fuels.

McCain’s effort to spotlight his involvement in international affairs and his qualifications for leading the United States in a dangerous world was relentless. He noted that he advised against President Reagan’s sending of troops to Lebanon in the 1980s. He said he supported the successful U.S. military actions in former Yugoslavia in the 1990s. He recalled that he has traveled to Georgia, the Georgian province of Abkhazia, Afghanistan and Pakistani Waziristan.

He touted meetings with U.S. generals and world leaders. “I have a record of being involved in these national security decisions,” he said.

When Obama brought up comments by Henry Kissinger that seemed different from McCain’s own views, McCain retorted that Kissinger has “been my friend for 35 years.”

McCain repeatedly questioned Obama’s understanding of how to handle world affairs, accusing him of not knowing the difference between strategy and tactics, saying Obama “doesn’t get it” and adding, “Again, a little bit of naiveté there.”

Obama sought to focus on McCain’s judgment, recalling a statement made by McCain about wiping out North Korea. He also hit repeatedly on the decision by Bush, which McCain supported, to begin the Iraq War. McCain tried to move the discussion to his backing for the surge in Iraq, prompting Obama to quip that McCain thought the war started in 2007.