I don't think it's a tough argument at all. The initial authorization for the invasion was timed to come to a vote immediately before the midterm elections, which Andy Card described in marketing terms. The run-up to the vote was critical for the Republican effort at the midterm, and without it the Senate would likely have not shifted back to the Republicans.

Murray Waas at the National Journal discussed how Rove used the war as a way to promote that image in advance of the 2004 campaign: Link

Only two months before Wilson went public with his allegations, the Iraq war was being viewed as one of the greatest achievements of Bush's presidency. Rove, whom Bush would later call the "architect" of his re-election campaign, was determined to exploit the war for the president's electoral success. On May 1, 2003, Bush made a dramatic landing on the flight deck of the USS Abraham Lincoln to announce to the nation the cessation of major combat operations in Iraq. Dressed in a military flight suit, the president emerged from a four-seat Navy S-3B Viking with the words "George W. Bush Commander-in-Chief" painted just below the cockpit window.

The New York Times later reported that White House aides "had choreographed every aspect of the event, even down to the members of the Lincoln crew arrayed in coordinated shirt colors over Mr. Bush's right shoulder and the 'Mission Accomplished' banner placed to perfectly capture the president and the celebratory two words in a single shot."

The Houston Chronicle noted back in 2003 that Rove had explicitly stated that military action would likely improve Republican midterm election results (while at the same time saying the invasion was not about politics). Link

Last year, Rove drew fire from Democrats for telling the Republican National Committee that the White House planned to use the war on terrorism to win the fall elections.

"We can go to the country on this issue, because they trust the Republican Party to do a better job of protecting and strengthening America's military might and thereby protecting America," Rove had said at an Austin meeting of the RNC.

Democratic Chairman Terry McAuliffe called Rove's remarks "shameful," but the strategy played out in ballot-box victories for the GOP. The Republican Party solidified its hold on the U.S. House and regained a slim Senate majority.

As the Republican Party pushed the war on terrorism as an issue, President Bush began pressing for Iraq to disarm. But the president made the decision to attack Iraq this week along with Britain after failing to win U.N. support for military action against Iraq.

U.S. forces this week began an attack on Iraq to drive Saddam out of power. President Bush has described Saddam as a threat to national security because he might arm terrorists like those who attacked New York City and Washington, D.C., on Sept. 11, 2001.

Polls clearly indicated that the Republican political advantages were greatest on Iraq and terrorism in 2002-2005. Focusing national politics on those issues was critical for the Republicans and the administration in the 2002 and 2004 elections. Link

Remember, Bush started out with marginal numbers, and was shaping up to be hammered on economic issues in '02 and '04 Link. 9/11 made foreign issues the top focus of the electorate, but everyone was behind Afghanistan--the President came out looking good, but the party he needed to advance his agenda (remember, the Senate was Democratic at the time) wasn't in a particularly favored position because of it. Every single Senate Democrat had supported the invasion of Afghanistan, and it looked like the situation there was stable enough to let voters put it aside during the midterms. Since both parties backed it strongly, it was impossible for the Republicans to gain any real separation on the issue from the Democrats. Iraq changed that dynamic, allowing the Republicans to claim dovishness on the part of Dems during the midterms, leading to the historic results.

But after the Republicans won in 2002, Bush was left with the dilemma of what to do next. He had wanted to topple Saddam since taking office (Paul O'Neill makes the case in his book), and now, by virtue of having had his party campaign on the issue only months before, he was handed the opportunity to take out Saddam and propel foreign policy to the top of the agenda again, only now for the 2004 elections.