In one corner stands the Senate’s most endangered incumbent.  In the other stands the country’s most criticized Senate challenger.  This race may end up determining the outcome when an eminently stoppable force meets an eminently movable object — and according to Rasmussen, the two objects are closing in on one another:

The fallout appears to linger in the Missouri Senate race, with incumbent Democrat Claire McCaskill still holding a six-point lead over Republican challenger Todd Akin. But the race is tightening.

The latest Rasmussen Reports telephone survey finds McCaskill will 49% support to Akin’s 43%. Four percent (4%) prefer some other candidate in the contest, and another four percent (4%) are undecided. (To see survey question wording, click here.)

Akin has rebounded slightly from late August when he trailed McCaskill 48% to 38% just after he told a television interviewer that in cases of “legitimate rape,” women’s reproductive systems shut down to prevent pregnancy. The resulting uproar prompted Mitt Romney and other leading Republicans to call for Akin to step down as the party’s Senate candidate in Missouri, but he refused.

While 49% represents McCaskill’s best showing in the race to date, Missouri now moves from Safe Democrat to Leans Democrat in the Rasmussen Senate Balance of Power rankings.

Interestingly, Akin only has a 15-point deficit among women now, an improvement of five points from just three weeks ago.  Akin has lost significant ground in that time with younger voters, declining from 32/45 in the 18-39YO demo to 30/60 today as that vote solidifies. He’s also slid among independents, albeit less dramatically, from 39/39 to 36/47.  However, Akin has retaken the lead in the other two age demos, 51/43 among 40-64YOs and 49/45 among seniors.  In August, those numbers were 41/49 and 40/52.

Akin’s regained a little ground on favorability, but not much.  His net favorability in August was -28 at 35/63, with 47% rating him “very unfavorable” while only 11% rated him “very favorable.”  Today he’s at -17, a gain of 11 points, at 39/56 — but 42% still rate him “very unfavorable.” He’s still cratered among independents at 30/61.

With all that said, how can McCaskill not be breaking this race wide open?  She has a +1 at 49/48, about the same as last month’s 48/48, which means that Akin’s misfortune hasn’t really been a boon to her personal standing.  Her own standing among independents isn’t all that much better than Akin’s at 41/54.

So here’s the bottom line.  Any other Democrat would have put Akin away — and any other Republican would have done the same to McCaskill.  This race may come down to which candidate can go longest without stepping on his or her own tongue.  The internal momentum suggests that Akin might end up recapturing his lost ground with a near-perfect campaign from here on out.