The dynamic appeared again Monday, when the president announced a new proposal to extend for one year Bush-era tax cuts for those making less than $250,000. The offer is tied more to Obama’s re-election campaign than his official duty as president, but he nonetheless was able to use his bully pulpit at the White House to make the announcement. An equivalent decision from the Republican presidential hopeful, who of course has no formal role in the Capitol Hill negotiations, would have been held in Ohio or Colorado, at a campaign rally lacking the same oomph. …

The China announcement also highlighted how the president can use the White House not just for theater, but – more importantly – to introduce new issues. The two best examples are among the biggest developments of the campaign: Obama’s decisions to support gay marriage and to allow illegal immigrants brought to the country as children to stay here legally. The politics of the former remain uncertain, but the latter, if it can intensify Obama’s support among Hispanics, might ultimately prove one of the key moments of the presidential race.

Romney, still just a candidate, can’t take any equivalent action. And consequently the president’s moves have often put him on the defensive, forcing him to discuss topics — such as gay marriage and immigration — that he’d rather avoid.