Steve Kornacki: Harris’ campaign could draw undecided voters off the fence — in both directions

Kamala Harris is launching her White House bid pretty much where Joe Biden left off: a few points behind Donald Trump nationally.

Democrats obviously hope that Harris' presidential campaign rollout will change how voters view her and this race, producing a meaningful polling improvement. And a new poll from Reuters/Ipsos (showing Harris at 44% among registered voters and Trump at 42%) very modestly, and tentatively, gives fuel to their optimism.

But previous polling hints at what could be a potentially significant difference in this new matchup. Essentially, they suggest that, faced with a Harris-Trump contest, the number of voters ready to pick sides may go up.

Take our own national NBC News survey, conducted two weeks ago. Against Biden, Trump led 45% to 43%; against Harris, Trump was ahead 47% to 45% (both results within the margin of error). It’s the same two-point spread, but Harris’ vote share is two points higher than Biden’s, just as Trump’s increases by two points with Harris as an opponent.

Similar shifts can be found elsewhere. A Quinnipiac University poll conducted mostly before Biden’s exit and released Monday, for instance, had Trump leading Biden 48% to 45%; with Harris subbed in, the result was 49% to 47% in favor of Trump. And a Morning Consult poll conducted after Biden’s withdrawal had Trump up 47% to 45% against Harris, while its previous survey had Trump ahead of Biden 47% to 41%.

In total, six major polls over the last month have found that the combined vote share in a Harris-Trump trial heat is higher than in a Biden-Trump one:

Not all recent polls have found this, though a big reason is that several prominent pollsters ask undecided voters which candidate they are leaning toward and then record