From a look at the #s, Thompson pollster John McLaughlin thinks so — that the relative late entry won’t be a problem in the end. From a memo he sent out today, he points out:

Based on our review of exit polling data from years like 1996 and 2000 where there was an open GOP seat, significant percentages of voters decided for whom they would vote in the final week leading up to Election Day.
Iowa – 1996
Decided Who To Vote For In…
Last 3 Days 23%
Last Week 19% (42% cumulative)
1996 CNN/VNS Exit Poll Data
New Hampshire – 1996
Decided Who To Vote For In…
Election Day 23%
Last 3 Days 20% (43% cumulative)
Last Week 22% (65% cumulative)
1996 CNN/VNS Exit Poll Data
New Hampshire – 2000
Decided who to vote for in…
Election Day 14%
Last 3 Days 12% (26% cumulative)
Last Week 24% (50% cumulative)
2000 CNN Exit Poll Data
South Carolina – 1996
Decided Who To Vote For In…
Today 17%
Last 3 Days 14% (31% cumulative)
Last Week 24% (55% cumulative)
1996 CNN/VNS Exit Poll Data
South Carolina – 2000
When Did You Decide To Vote?
Today 9%
Last 3 Days 10% (19% cumulative)
Last Week 19% (38% cumulative)
2000 CNN Exit Poll Data