After leaving Dundalk for Belfast last night, President Clinton passed the south Armagh hills on which the British army watchtowers so hateful to republicans are sited.
Mr Clinton is sufficiently briefed to know that the prospects of the political deadlock being broken hinge on a British willingness to start dismantling these observation posts. He also knows that this will involve a trade-off from the IRA on arms.
It's the quid-pro-quo routine. Locked into this sequencing arrangement is an end to David Trimble's ban on Sinn Fein ministers doing official NorthSouth ministerial business, and policing.
So, having taken risks for Gerry Adams while being careful not to antagonise David Trimble, is Mr Clinton now destined to leave Northern Ireland tonight without any Christmas gifts that amount to a deal or, at least, point to real potential for a deal?
Judging by the word from senior British and Irish sources last night, the emphasis is on the latter, on Tony Blair, Gerry Adams, David Trimble and Seamus Mallon in their talks with Mr Clinton at Stormont today attempting to lay the foundation for a breakthrough.
Dublin and London sources were cautious last night. "Let's not get ahead of ourselves," said a London insider. "Let's not build up expectations in case they fall flat," was the line from Dublin.
But there was consensus that the talks at Parliament Buildings this morning are important. Top-notch British and Irish officials have been punching in the hours with each other and with the key players in recent days trying to develop a loose but common approach that, with Mr Clinton's "can-do" influence, could be hardened at Stormont today.
There is a whiff of a willingness from the British side to start toppling the south Armagh towers, but only based on a reciprocal willingness from the IRA to re-engage with Gen John de Chastelain's decommissioning body.
Furthermore, London and Mr Trimble want greater detail on how the IRA would meet its commitment to put its arms verifiably beyond use.
If those two difficult issues can be unlocked, then Mr Trimble's veto on Martin McGuinness and Bairbre de Brun automatically ends. However, were the IRA to move, republicans would also require some guarantees that any gesture made would not be rebuffed at the next Ulster Unionist Council meeting.
A senior republican source last night was downbeat about the prospects of serious movement today.
Interestingly, he mused that January might be a more strategic time for a deal, because a sequencing package then might put David Trimble in a better position to win the UUC battle that is expected next month.
Then we're left with policing. Peter Mandelson was expected to publish his Police Act implementation plan at the end of this week, but such was the depth of opposition to a draft of the plan witnessed by Seamus Mallon that the Northern Secretary has retreated to the drawing board to determine if the SDLP can be assuaged.
The British believe that most of the Mr Mallon's seven demands on policing can be met, although at the moment the SDLP is engaged in serious hardballing.
Publication of the implementation plan may be briefly put back as efforts continue to win SDLP support for the Police Act, one British source suggested.
If the SDLP buys into the Act, then the much more problematic question is, will Sinn Fein at least test the police reform deal?
"Everybody knows the makings of a package but there's no point in rushing into an artificial deadline because of Bill Clinton's visit," said one London insider last night, echoing a general view.
So, the focus last night was on the President spurring the politicians to settle their outstanding differences and anchor the Belfast Agreement in the weeks ahead, rather than on immediately solving outstanding problems.
But despite the caution, there was still some lingering hope that the President will not leave for London totally empty-handed tonight. We should know for sure when Mr Clinton delivers his keynote address at the new Odyssey centre in Belfast this afternoon.