This is a really, really tough one, but I'm gonna go with a very heavy qualified "yes, sometimes".
Obviously the other answer's citation to Rule 11 is valid (and I believe most if not all state courts have similar rules) and well taken. But it's far from dispositive here.
There are plenty of scenarios where delay is beneficial to the client, and can be effected legally and ethically, and therefore the lawyer indeed has a duty to pursue it if it's good strategy. There are also plenty of cases where delay is purely dilatory and bad faith, and thus the lawyer has a duty not to pursue it. Therefore you really need every relevant fact to know which is which. However, I'll give three hypotheticals to try to demonstrate where the line is between delay-as-a-strategy being a valid one vs. not.
1) The defendant has a good faith and persuasive basis to argue the proceedings should be delayed, and offers that exact reason to the court.
You have a case that turns on an issue currently before the U.S. Supreme Court that's likely to be resolved in 1-2 months. If the SCOTUS case comes out in your favor, the current case will almost certainly be dismissed. If not, your client will clearly lose the current case if it goes to trial, so it will settle or plead instead. Transparency is the clear winner here - point out the pending Supreme Court case to the trial court and ask for a delay until at least the end of June or the issuance of the opinion, explaining exactly why. This will 100% be up to the trial court's discretion, but I think most judges would grant it, especially if there's not a pattern/history of delay tactics on the part of the defense. No one wants to waste judicial resources on a case that could soon be moot. Is it self-serving? Absolutely, but so is nearly everything a lawyer argues in court, and the lawyer would probably be negligent if they didn't make this request and just went to trial instead.
2) The defendant has valid avenues of delay, e.g., motion practice, that are probably losers, and that probably wouldn't get made (due to cost) if delay weren't in the party's interest or the party didn't have the resources, but they aren't objectively frivolous.
For better or worse, a defendant with the resources has myriad completely legal and ethical avenues to extend the lifetime of a case. Motions to dismiss. Permissive counterclaims. Motions to compel discovery. Motions for summary judgment. Motions in limine. Daubert motions. Potential interlocutory appeals. Regular appeals. The list is quite extensive.
Despite the literal wording of Rule 11, courts as a general matter do not - because they usually cannot - try to ascertain the subjective tactical or strategic motivation of any particular move in a litigation. Doing so would usually require piercing the privilege which courts are loathe to do. The conduct would have to be absolutely egregious and repetitive. As long as a motion or other move has a conceivably legitimate purpose and a non-zero chance of success, the subjective reason for its filing, how it fits into the litigation strategy, etc., is not going to be questioned and is in fact a privileged matter between the lawyer and the client. The lawyer will be given the benefit of the doubt and a legitimate purpose presumed, almost always.
If, indeed, you as a lawyer file a motion with little expectation of success, and the primary strategic value you see in doing so is delay, is that technically an ethical violation of your duty to the court? Maybe theoretically yes, but it's really between you and your conscience at that point. It happens all the time and it's essentially impossible to prevent without gutting due process. Yes, I have done it (rarely), and in the cases I did it, I don't regret it. I've also had it done to me, and in at least one case I empathized with the lawyer doing it and the result actually worked to everyone's benefit.[1]
What I would say here is that the lawyer does not necessarily have an affirmative duty to use this strategy, but they won't face discipline for doing so either (unless of course they're just wasting their client's money against the client's wishes). This case (by design) falls in the middle and is tough.
3) Delay is attempted either through repetitive frivolous litigation moves, or through extrajudicial means.
Motions or pleadings that have zero chance of success - a controlling appellate opinion is directly on point - or made repetitively via motions for reconsideration that offer no new facts or arguments, will clearly cross the line. Not only does the lawyer not have a duty to do this, they have a duty not to.
Another category of delay tactic is also clearly unethical and potentially illegal - using extrajudicial means to try to delay a case. For example, a lawyer might try to get a witness to leave the jurisdiction for an extended vacation so they can't be deposed or be available for trial. Absolutely unethical and (while I never did criminal law) might even constitute obstruction of justice.
So there you have it. I realize the question is about a particular politician defendant trying to delay a case until after a particular election, and I'm definitely not gonna go there, but I hope it's clear that the issue is far from open and shut.
[1] We were trying to collect on an open and shut debt, and the defense was trying to delay as long as possible, claiming the defendant was just trying to gather up the money (which we didn't believe). But in fact, once we finally did get a final judgment we could start enforcing, the defendant came up with the money. Maybe he had it the whole time, or maybe the delay really did give him more time to muster it. We'll never know.
