For both parties, impeachment has mutated into the latest in a long series of base-rallying exercises.

The Senate impeachment trial of President Trump begins in earnest Tuesday, almost precisely four months since House Speaker Nancy Pelosi announced the start of an inquiry into allegations that the president had committed Treason, Bribery, or other high Crimes and Misdemeanors by manipulating military aid to Ukraine for personal political advantage.
Little uncertainty surrounds the likely outcome: acquittal for Trump by a Republican-led Senate.
On the other big question, though how impeachment might affect the 2020 election there is more room for debate. Whats striking so far is how little difference this supposedly historic process seems to be making.
The main impact has been to reinforce what was already the central issue in U.S. politics: Donald Trump, pro or con? Now more than ever, opposition to Trump defines what it means to be a Democrat and support for him defines what it means to be a Republican.
Support for impeachment rose from 71.9 percent among Democrats the day before Pelosis Sept. 24 announcement to 86.3 percent today, whereas Republican support for it has hardly budged, according to the FiveThirtyEight average of polls.
Pelosi herself led the anti-impeachment forces in the party, warning progressive pro-impeachment Democrats after the party regained the House majority in 2018 that impeaching Trump would divide the country, unless evidence of presidential wrongdoing was so strong that Republicans also voted to impeach.
Pelosi and other old Democratic hands feared a voter backlash that could cost them seats in the House, just as the GOP House majority shrank by five seats in 1998 amid the impeachment of Democratic President Bill Clinton.
In the end, the Ukraine revelations forced Pelosis hand and, contrary to her initial fears, a party-line impeachment may help House Democrats, or at least not hurt them.
Yes, Democratic Rep. Jeff Van Drew of a deep-red New Jersey district switched parties in December rather than vote to impeach, but 30 other Democrats who represent swing districts (except for Collin C. Peterson of Minnesota and Jared Golden of Maine) backed both articles of impeachment, a pretty good indication that, for them, the political benefits including a flow of campaign cash from progressive donors outweigh the costs.
And there is little sign of major losses for Democrats next year, let alone that the House is at risk. The party holds a 5.8 percentage point edge in the generic ballot for House races in 2020, according to FiveThirty­Eight, down only modestly from the 8.6 point margin by which they beat Republicans in 2018.
At the presidential level, meanwhile, impeachment has done essentially nothing to Trumps standing with the public. The day before Pelosi announced the inquiry, 43.3 percent of registered or likely voters approved of the job he was doing; 43.9 percent approve today, while the share disapproving, now 52.1 percent, represents a 1.2 point drop since the eve of her announcement.
Near-total Republican opposition to Trumps removal from office, via a Senate conviction, cancels out near-total Democratic support for it, with the result that the public is essentially tied on that issue, though the most recent survey, by Gallup, shows the public opposing removal by 51 to 46 percent.
As for the Senate, Democrats have high hopes that impeachment can help them regain control of the body, which Republicans control 53 to 47, even if there is little or no chance of getting the requisite 67 votes to oust the president.
Hence they are using the impending trial to focus their supporters ire on a man Democrats love to hate: Majority Leader Mitch McConnell (just as Republicans turned the House impeachment into a fundraising campaign focused on the detested Pelosi).
They also hope to stage a series of votes on procedural issues especially the key question of whether to call additional witnesses that will put GOP senators facing difficult reelection campaigns on the spot.
So far, impeachment seems to be forcing swing-state Republicans Martha McSally (Ariz.), Thom Tillis (N.C.), Joni Ernst (Iowa) and Cory Gardner (Colo.) further into the arms of McConnell and the right-wing, pro-Trump forces that dominate the party.
All of the above were scheduled to join the majority leader and Sen. Rick Scott for three keep the Senate red fundraisers in Scotts home state of Florida on Tuesday but the events had to be postponed because of the start of the Senate trial. Significantly, moderate Republican Sen. Susan Collins of Maine, who has said she is open to calling witnesses after each sides opening arguments, was slated to join.
Still angry at Democratic attacks over her support for Supreme Court Justice Brett M. Kavanaugh, Collins has sounded unusually partisan Republican notes of late, including her acidic response to pressure on the witness issue from Senate Minority Leader Charles E. Schumer (D-N.Y.).
I dont think hes really very interested in doing anything but trying to defeat me by telling lies to the people of Maine, Collins said.
The political middle ground upon which Collins built her career is vanishing. For both Democrats and Republicans, impeachment has mutated into the latest in a long series of base-rallying exercises, in preparation for a November 2020 election that will have almost nothing to do with persuading undecideds and everything to do with mobilizing partisans.
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