In recent weeks he’s taken his sales pitch to Arkansas, Illinois, Oklahoma, Louisiana and California. Next on the list: a noon rally in a favorite place, Annapolis, Md.

I’m not talking about President Bush. I’m talking about Sen. John McCain, who is still in campaign mode (he never abandoned it) and who is, therefore, likely to be as big a pain in the butt to the president this year as any Democrat.

Maybe more.

I don’t mean that McCain is running for president. It’s both more and less than that. McCain regards himself as a man on a mission, leader of a crusade with an independent base. On campaign reform and other issues-chief among them tax cuts and defense policy-McCain has clout and credibility and could be on a collision course with the White House. One other thing: There is no love lost between Bush and McCain, genial photo ops aside.

Bush can’t afford unnecessary fights with Republicans, even one as ornery and ungovernable as McCain. GOP control of Congress is too shaky. For now, Bush’s job-approval numbers are more than respectable, given the bitter election of 2000. But they won’t be solidified by battling with the likes of McCain.

McCain hits center stage on Monday, as the Senate begins at least two weeks of debate on his (and Sen. Russ Feingold’s) campaign-finance reform bill. This is McCain’s holy grail, and has been for years. He and Feingold-and their 58 cosponsors-think their bill will greatly reduce the role of Big Money in politics.

That’s debatable, but it’s only because of McCain’s persistence that the debate will take place at all. And it won’t be a perfunctory discussion. The rules call for unlimited debate, and lots of amendments. For once the Senate could well be the “world’s greatest debating society” of hallowed legend.

Neither President Bush nor Republican Senate leaders want to limit the flow of “soft money” to political parties. A growing number of advocacy groups-from right-to-lifers to labor unions-fear McCain-Feingold would limit their ability to advertise and thus their free-speech rights. Democrats, free for years to cast grandstanding votes in favor of the bill (in sure knowledge it didn’t have the numbers to pass), can’t do that anymore.

It’ll be close.

But, in human terms, the more interesting drama is the unresolved and probably unresolvable conflict between Bush and McCain. It was the major story line on the campaign trail in 2000, and it’ll remain that way in Planet Washington.

That simmering conflict affects not only the fate of campaign-finance reform, but other major issues as well. Take tax cuts. McCain has been conspicuously hesitant about supporting the president’s $1.6 trillion, 10-year plan. The senator expresses concern about the true size of future surpluses, and about the sanctity of Social Security and Medicare. In a 50-50 Senate, every GOP vote is obviously crucial. For now only GOP “moderates,” most of them from the Northeast, are holding out for a smaller tax cut. McCain’s role will be crucial in holding the line for the White House-or in forcing wholesale revisions.

The same with defense policy, where McCain’s special story-Annapolis grad, Vietnam War prisoner, Navy lobbyist on the Hill-gives his views great heft. Bush’s budget depends on streamlining the Pentagon: on somehow making the armed forces simultaneously more potent and less costly. It’s hard to see how such Big Think succeeds without McCain’s input and support.

Bush has tried to handle McCain carefully-like a package of high-density explosives. The president and Senate Majority Leader Trent Lott agreed to give McCain time for his campaign-finance debate early in the session, before the big season-ending debates on taxes and the budget (and during various schools’ spring break schedules).

Handling him will get harder from here. McCain believes that his run for the presidency was more than a campaign. The name of his PAC, Straight Talk America, speaks for itself. It’s raised the dough that has kept him on the road. His campaign crew, brought together like veterans of Normandy, are intact and in touch.

McCain’s perch as chairman of the Senate Commerce Committee gives him a platform to conduct high-profile hearings on all manner of issues-from TV sleaze to airline delays. Eventually, inevitably, his hearings won’t be about industry screw-ups alone. Sooner or later, they’ll also be about the track record of the administration-the Bush Administration-in ameliorating those problems.

And then there is, for want of a better word, the primal level. Though the GOP primaries are ancient history, they’ll never be forgotten by McCain and his acolytes. They thought the Bush crowd played too hard, and too dirty, in places such as South Carolina. The McCainanites think They Wuz Robbed. It’s a matter of faith.

Fair fight or not, McCain hates to lose-just as much as he hates to be ignored. At the start of the 1999 campaign season he felt that I wasn’t taking his campaign seriously enough. We got into a friendly little dust-up about it on the “Imus in the Morning” radio and MSNBC Cable show. He pretty much had me stammering defensively on the air. He was right, of course, as subsequent developments showed.

Later that day, a carton was hand-delivered from his office. I opened it and found a pair of bright-red leather Everlast boxing gloves. They were signed, “John McCain-The Champ.” And that’s the man: He’s not in the White House. He’s not, in fact, The Champ. But he’s still in the ring, and still throwing jabs.