In an address to foreign-policy experts and community leaders in Detroit, Mr Clinton insisted that the United States would be "safer and stronger" with enlargement. Nor would it pose any threat to non-members, he declared, in a new effort to defuse Russia's continuing misgivings about the scheme, which have led Moscow to threaten not to ratify the Salt-2 arms-reduction treaty if Nato was expanded closer to its borders.
Now, after a long period of keeping its exact options open, the administration has finally set a firm target date for enlargement, choosing the year that marks the 50th anniversary of Nato's creation, and the 10th anniversary of the breach of the Berlin wall, the event which above all other symbolises the end of the Cold War.
In his first real foreign- policy foray of the presidential election campaign, Mr Clinton furthermore made it clear that after the initial group of entrants, other countries could join later: "Nato will remain open to all of Europe's emerging democracies who are ready to shoulder the responsibilities of membership." Nobody would be automatically excluded, he said, "no country outside Nato will have a veto".
The President did not name the countries likely to be formally invited to join at a summit of the alliance next year, the exact date of which will be set by a Nato ministerial meeting this December. But the first group is expected to consist of Poland, Hungary, the Czech Republic, and possibly Slovenia.
Mr Clinton's goal yesterday was to project himself as a statesman above the campaign- trail hurly-burly. But by no coincidence, he chose for the announcement the industrial Midwest, home to many voters from east European ethnic groups who instinctively favour anything that protects their old homelands against Russia, and who are always a factor to be reckoned with in electorally pivotal states such as Michigan.
Not that Mr Clinton needs to make a special pitch, if a new New York Times/CBS poll which gives him a massive 24-point lead over his Republican challenger, Bob Dole, is anything to go by. Every sign is that Mr Dole's eleventh-hour decision to attack Mr Clinton's character is backfiring, resurrecting the "old Bob Dole" of unsmiling political hatchetman and blurring the assiduously cultivated image of conciliatory and wise leader.
Such considerations, however, did not prevent a scathing response to Mr Clinton's proposal. The administration, he said, "has been dragging its feet on expansion". Not only should negotiations with Poland, Hungary and the Czech Republic begin at once, with a 1998 deadline for entry, but the alliance should give separate assurances to the Baltic states and Ukraine. This was "particularly important given the ongoing instability in Russia".
In fact, the Dole broadside obscures the fact that on most foreign-policy issues, he has scarcely a serious difference with the President. Both are free traders. Both seek to foster a market economy in Russia, and bind the former superpower rival closer to the Western democracies. Both are opposed to isolating China. Both favour a tough line on Fidel Castro's Cuba and Saddam Hussein's Iraq. Mr Dole backed the Dayton accords, which brought a settlement to Bosnia, and has outbid even Mr Clinton in expressions of support for Israel.
Nor would Mr Dole quarrel with the President's twin-track policy on Nato, combining insistence that enlargement must go ahead whatever Russia's feelings and strenuous efforts to make sure Moscow does not feel isolated or threatened. A mechanism should be set for regular Nato-Russia meetings "at all levels", Mr Clinton said, implying regular summits between Russian and Western leaders on security issues.
The foreign-policy speech came on another hectic day of fund-raising and campaigning by Mr Clinton, which would end with another trip to Florida, a normally Republican state which the Democrats have high hopes of capturing in 1996.
With less than a fortnight to election day, the President is, if anything, widening his lead over Mr Dole, who now displays his old fault of inability to focus on any one issue for long. His campaign has acquired a random, scattershot feel, and its mood has not been improved by reports of disagreement with his running-mate, Jack Kemp.
According to reports, naturally flatly denied by those concerned, the supply-sider Mr Kemp has pleaded in vain with Mr Dole to concentrate on the Republican proposal of a 15 per-cent across-the-board tax cut. Mr Dole's embrace of the idea never quite rang true. These days, the plan rarely rates more than a perfunctory mention in his speeches.